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Types of Literature Review — A Guide for Researchers

Table of Contents

Researchers often face challenges when choosing the appropriate type of literature review for their study. Regardless of the type of research design and the topic of a research problem , they encounter numerous queries, including:

What is the right type of literature review my study demands?

• How do we gather the data?
• How to conduct one?
• How reliable are the review findings?
• How do we employ them in our research? And the list goes on.

If you’re also dealing with such a hefty questionnaire, this article is of help. Read through this piece of guide to get an exhaustive understanding of the different types of literature reviews and their step-by-step methodologies along with a dash of pros and cons discussed.

Heading from scratch!

What is a Literature Review?

A literature review provides a comprehensive overview of existing knowledge on a particular topic, which is quintessential to any research project. Researchers employ various literature reviews based on their research goals and methodologies. The review process involves assembling, critically evaluating, and synthesizing existing scientific publications relevant to the research question at hand. It serves multiple purposes, including identifying gaps in existing literature, providing theoretical background, and supporting the rationale for a research study.

What is the importance of a Literature review in research?

Literature review in research serves several key purposes, including:

• Background of the study: Provides proper context for the research. It helps researchers understand the historical development, theoretical perspectives, and key debates related to their research topic.
• Identification of research gaps: By reviewing existing literature, researchers can identify gaps or inconsistencies in knowledge, paving the way for new research questions and hypotheses relevant to their study.
• Theoretical framework development: Facilitates the development of theoretical frameworks by cultivating diverse perspectives and empirical findings. It helps researchers refine their conceptualizations and theoretical models.
• Methodological guidance: Offers methodological guidance by highlighting the documented research methods and techniques used in previous studies. It assists researchers in selecting appropriate research designs, data collection methods, and analytical tools.
• Quality assurance and upholding academic integrity: Conducting a thorough literature review demonstrates the rigor and scholarly integrity of the research. It ensures that researchers are aware of relevant studies and can accurately attribute ideas and findings to their original sources.

Types of Literature Review

Literature review plays a crucial role in guiding the research process , from providing the background of the study to research dissemination and contributing to the synthesis of the latest theoretical literature review findings in academia.

However, not all types of literature reviews are the same; they vary in terms of methodology, approach, and purpose. Let's have a look at the various types of literature reviews to gain a deeper understanding of their applications.

1. Narrative Literature Review

A narrative literature review, also known as a traditional literature review, involves analyzing and summarizing existing literature without adhering to a structured methodology. It typically provides a descriptive overview of key concepts, theories, and relevant findings of the research topic.

Unlike other types of literature reviews, narrative reviews reinforce a more traditional approach, emphasizing the interpretation and discussion of the research findings rather than strict adherence to methodological review criteria. It helps researchers explore diverse perspectives and insights based on the research topic and acts as preliminary work for further investigation.

Steps to Conduct a Narrative Literature Review

Source:- https://www.researchgate.net/figure/Steps-of-writing-a-narrative-review_fig1_354466408

Define the research question or topic:

The first step in conducting a narrative literature review is to clearly define the research question or topic of interest. Defining the scope and purpose of the review includes — What specific aspect of the topic do you want to explore? What are the main objectives of the research? Refine your research question based on the specific area you want to explore.

Conduct a thorough literature search

Once the research question is defined, you can conduct a comprehensive literature search. Explore and use relevant databases and search engines like SciSpace Discover to identify credible and pertinent, scholarly articles and publications.

Select relevant studies

Before choosing the right set of studies, it’s vital to determine inclusion (studies that should possess the required factors) and exclusion criteria for the literature and then carefully select papers. For example — Which studies or sources will be included based on relevance, quality, and publication date?

*Important (applies to all the reviews): Inclusion criteria are the factors a study must include (For example: Include only peer-reviewed articles published between 2022-2023, etc.). Exclusion criteria are the factors that wouldn’t be required for your search strategy (Example: exclude irrelevant papers, preprints, written in non-English, etc.)

Critically analyze the literature

Once the relevant studies are shortlisted, evaluate the methodology, findings, and limitations of each source and jot down key themes, patterns, and contradictions. You can use efficient AI tools to conduct a thorough literature review and analyze all the required information.

Synthesize and integrate the findings

Now, you can weave together the reviewed studies, underscoring significant findings such that new frameworks, contrasting viewpoints, and identifying knowledge gaps.

Discussion and conclusion

This is an important step before crafting a narrative review — summarize the main findings of the review and discuss their implications in the relevant field. For example — What are the practical implications for practitioners? What are the directions for future research for them?

Write a cohesive narrative review

Organize the review into coherent sections and structure your review logically, guiding the reader through the research landscape and offering valuable insights. Use clear and concise language to convey key points effectively.

Structure of Narrative Literature Review

A well-structured, narrative analysis or literature review typically includes the following components:

• Introduction: Provides an overview of the topic, objectives of the study, and rationale for the review.
• Background: Highlights relevant background information and establish the context for the review.
• Main Body: Indexes the literature into thematic sections or categories, discussing key findings, methodologies, and theoretical frameworks.
• Discussion: Analyze and synthesize the findings of the reviewed studies, stressing similarities, differences, and any gaps in the literature.
• Conclusion: Summarizes the main findings of the review, identifies implications for future research, and offers concluding remarks.

Pros and Cons of Narrative Literature Review

• Flexibility in methodology and doesn’t necessarily rely on structured methodologies
• Follows traditional approach and provides valuable and contextualized insights
• Suitable for exploring complex or interdisciplinary topics. For example — Climate change and human health, Cybersecurity and privacy in the digital age, and more
• Subjectivity in data selection and interpretation
• Potential for bias in the review process
• Lack of rigor compared to systematic reviews

Example of Well-Executed Narrative Literature Reviews

Paper title:  Examining Moral Injury in Clinical Practice: A Narrative Literature Review

Source: SciSpace

While narrative reviews offer flexibility, academic integrity remains paramount. So, ensure proper citation of all sources and maintain a transparent and factual approach throughout your critical narrative review, itself.

2. Systematic Review

A systematic literature review is one of the comprehensive types of literature review that follows a structured approach to assembling, analyzing, and synthesizing existing research relevant to a particular topic or question. It involves clearly defined criteria for exploring and choosing studies, as well as rigorous methods for evaluating the quality of relevant studies.

It plays a prominent role in evidence-based practice and decision-making across various domains, including healthcare, social sciences, education, health sciences, and more. By systematically investigating available literature, researchers can identify gaps in knowledge, evaluate the strength of evidence, and report future research directions.

Steps to Conduct Systematic Reviews

Source:- https://www.researchgate.net/figure/Steps-of-Systematic-Literature-Review_fig1_321422320

Here are the key steps involved in conducting a systematic literature review

Formulate a clear and focused research question

Clearly define the research question or objective of the review. It helps to centralize the literature search strategy and determine inclusion criteria for relevant studies.

Develop a thorough literature search strategy

Design a comprehensive search strategy to identify relevant studies. It involves scrutinizing scientific databases and all relevant articles in journals. Plus, seek suggestions from domain experts and review reference lists of relevant review articles.

Screening and selecting studies

Employ predefined inclusion and exclusion criteria to systematically screen the identified studies. This screening process also typically involves multiple reviewers independently assessing the eligibility of each study.

Data extraction

Extract key information from selected studies using standardized forms or protocols. It includes study characteristics, methods, results, and conclusions.

Critical appraisal

Evaluate the methodological quality and potential biases of included studies. Various tools (BMC medical research methodology) and criteria can be implemented for critical evaluation depending on the study design and research quetions .

Data synthesis

Analyze and synthesize review findings from individual studies to draw encompassing conclusions or identify overarching patterns and explore heterogeneity among studies.

Interpretation and conclusion

Interpret the findings about the research question, considering the strengths and limitations of the research evidence. Draw conclusions and implications for further research.

The final step — Report writing

Craft a detailed report of the systematic literature review adhering to the established guidelines of PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). This ensures transparency and reproducibility of the review process.

By following these steps, a systematic literature review aims to provide a comprehensive and unbiased summary of existing evidence, help make informed decisions, and advance knowledge in the respective domain or field.

Structure of a systematic literature review

A well-structured systematic literature review typically consists of the following sections:

• Introduction: Provides background information on the research topic, outlines the review objectives, and enunciates the scope of the study.
• Methodology: Describes the literature search strategy, selection criteria, data extraction process, and other methods used for data synthesis, extraction, or other data analysis..
• Results: Presents the review findings, including a summary of the incorporated studies and their key findings.
• Discussion: Interprets the findings in light of the review objectives, discusses their implications, and identifies limitations or promising areas for future research.
• Conclusion: Summarizes the main review findings and provides suggestions based on the evidence presented in depth meta analysis.

*Important (applies to all the reviews): Remember, the specific structure of your literature review may vary depending on your topic, research question, and intended audience. However, adhering to a clear and logical hierarchy ensures your review effectively analyses and synthesizes knowledge and contributes valuable insights for readers.

Pros and Cons of Systematic Literature Review

• Adopts rigorous and transparent methodology
• Minimizes bias and enhances the reliability of the study
• Provides evidence-based insights
• Time and resource-intensive
• High dependency on the quality of available literature (literature research strategy should be accurate)
• Potential for publication bias

Example of Well-Executed Systematic Literature Review

Paper title: Systematic Reviews: Understanding the Best Evidence For Clinical Decision-making in Health Care: Pros and Cons.

Read this detailed article on how to use AI tools to conduct a systematic review for your research!

3. Scoping Literature Review

A scoping literature review is a methodological review type of literature review that adopts an iterative approach to systematically map the existing literature on a particular topic or research area. It involves identifying, selecting, and synthesizing relevant papers to provide an overview of the size and scope of available evidence. Scoping reviews are broader in scope and include a diverse range of study designs and methodologies especially focused on health services research.

The main purpose of a scoping literature review is to examine the extent, range, and nature of existing studies on a topic, thereby identifying gaps in research, inconsistencies, and areas for further investigation. Additionally, scoping reviews can help researchers identify suitable methodologies and formulate clinical recommendations. They also act as the frameworks for future systematic reviews or primary research studies.

Scoping reviews are primarily focused on —

• Emerging or evolving topics — where the research landscape is still growing or budding. Example — Whole Systems Approaches to Diet and Healthy Weight: A Scoping Review of Reviews .
• Broad and complex topics : With a vast amount of existing literature.
• Scenarios where a systematic review is not feasible: Due to limited resources or time constraints.

Steps to Conduct a Scoping Literature Review

While Scoping reviews are not as rigorous as systematic reviews, however, they still follow a structured approach. Here are the steps:

Identify the research question: Define the broad topic you want to explore.

Identify Relevant Studies: Conduct a comprehensive search of relevant literature using appropriate databases, keywords, and search strategies.

Select studies to be included in the review: Based on the inclusion and exclusion criteria, determine the appropriate studies to be included in the review.

Data extraction and charting : Extract relevant information from selected studies, such as year, author, main results, study characteristics, key findings, and methodological approaches.  However, it varies depending on the research question.

Collate, summarize, and report the results: Analyze and summarize the extracted data to identify key themes and trends. Then, present the findings of the scoping review in a clear and structured manner, following established guidelines and frameworks .

Structure of a Scoping Literature Review

A scoping literature review typically follows a structured format similar to a systematic review. It includes the following sections:

• Introduction: Introduce the research topic and objectives of the review, providing the historical context, and rationale for the study.
• Methods : Describe the methods used to conduct the review, including search strategies, study selection criteria, and data extraction procedures.
• Results: Present the findings of the review, including key themes, concepts, and patterns identified in the literature review.
• Discussion: Examine the implications of the findings, including strengths, limitations, and areas for further examination.
• Conclusion: Recapitulate the main findings of the review and their implications for future research, policy, or practice.

Pros and Cons of Scoping Literature Review

• Provides a comprehensive overview of existing literature
• Helps to identify gaps and areas for further research
• Suitable for exploring broad or complex research questions
• Doesn’t provide the depth of analysis offered by systematic reviews
• Subject to researcher bias in study selection and data extraction
• Requires careful consideration of literature search strategies and inclusion criteria to ensure comprehensiveness and validity.

In short, a scoping review helps map the literature on developing or emerging topics and identifying gaps. It might be considered as a step before conducting another type of review, such as a systematic review. Basically, acts as a precursor for other literature reviews.

Example of a Well-Executed Scoping Literature Review

Paper title: Health Chatbots in Africa Literature: A Scoping Review

Check out the key differences between Systematic and Scoping reviews — Evaluating literature review: systematic vs. scoping reviews

4. Integrative Literature Review

Integrative Literature Review (ILR) is a type of literature review that proposes a distinctive way to analyze and synthesize existing literature on a specific topic, providing a thorough understanding of research and identifying potential gaps for future research.

Unlike a systematic review, which emphasizes quantitative studies and follows strict inclusion criteria, an ILR embraces a more pliable approach. It works beyond simply summarizing findings — it critically analyzes, integrates, and interprets research from various methodologies (qualitative, quantitative, mixed methods) to provide a deeper understanding of the research landscape. ILRs provide a holistic and systematic overview of existing research, integrating findings from various methodologies. ILRs are ideal for exploring intricate research issues, examining manifold perspectives, and developing new research questions.

Steps to Conduct an Integrative Literature Review

• Identify the research question: Clearly define the research question or topic of interest as formulating a clear and focused research question is critical to leading the entire review process.
• Literature search strategy: Employ systematic search techniques to locate relevant literature across various databases and sources.
• Evaluate the quality of the included studies : Critically assess the methodology, rigor, and validity of each study by applying inclusion and exclusion criteria to filter and select studies aligned with the research objectives.
• Data Extraction: Extract relevant data from selected studies using a structured approach.
• Synthesize the findings : Thoroughly analyze the selected literature, identify key themes, and synthesize findings to derive noteworthy insights.
• Critical appraisal: Critically evaluate the quality and validity of qualitative research and included studies by using BMC medical research methodology.
• Interpret and present your findings: Discuss the purpose and implications of your analysis, spotlighting key insights and limitations. Organize and present the findings coherently and systematically.

Structure of an Integrative Literature Review

• Introduction : Provide an overview of the research topic and the purpose of the integrative review.
• Methods: Describe the opted literature search strategy, selection criteria, and data extraction process.
• Results: Present the synthesized findings, including key themes, patterns, and contradictions.
• Discussion: Interpret the findings about the research question, emphasizing implications for theory, practice, and prospective research.
• Conclusion: Summarize the main findings, limitations, and contributions of the integrative review.

Pros and Cons of Integrative Literature Review

• Informs evidence-based practice and policy to the relevant stakeholders of the research.
• Contributes to theory development and methodological advancement, especially in the healthcare arena.
• Integrates diverse perspectives and findings
• Time-consuming process due to the extensive literature search and synthesis
• Requires advanced analytical and critical thinking skills
• Potential for bias in study selection and interpretation
• The quality of included studies may vary, affecting the validity of the review

Example of Integrative Literature Reviews

Paper Title: An Integrative Literature Review: The Dual Impact of Technological Tools on Health and Technostress Among Older Workers

5. Rapid Literature Review

A Rapid Literature Review (RLR) is the fastest type of literature review which makes use of a streamlined approach for synthesizing literature summaries, offering a quicker and more focused alternative to traditional systematic reviews. Despite employing identical research methods, it often simplifies or omits specific steps to expedite the process. It allows researchers to gain valuable insights into current research trends and identify key findings within a shorter timeframe, often ranging from a few days to a few weeks — unlike traditional literature reviews, which may take months or even years to complete.

When to Consider a Rapid Literature Review?

• When time impediments demand a swift summary of existing research
• For emerging topics where the latest literature requires quick evaluation
• To report pilot studies or preliminary research before embarking on a comprehensive systematic review

Steps to Conduct a Rapid Literature Review

• Define the research question or topic of interest. A well-defined question guides the search process and helps researchers focus on relevant studies.
• Determine key databases and sources of relevant literature to ensure comprehensive coverage.
• Develop literature search strategies using appropriate keywords and filters to fetch a pool of potential scientific articles.
• Screen search results based on predefined inclusion and exclusion criteria.
• Extract and summarize relevant information from the above-preferred studies.
• Synthesize findings to identify key themes, patterns, or gaps in the literature.
• Prepare a concise report or a summary of the RLR findings.

Structure of a Rapid Literature Review

An effective structure of an RLR typically includes the following sections:

• Introduction: Briefly introduce the research topic and objectives of the RLR.
• Methodology: Describe the search strategy, inclusion and exclusion criteria, and data extraction process.
• Results: Present a summary of the findings, including key themes or patterns identified.
• Discussion: Interpret the findings, discuss implications, and highlight any limitations or areas for further research
• Conclusion: Summarize the key findings and their implications for practice or future research

Pros and Cons of Rapid Literature Review

• RLRs can be completed quickly, authorizing timely decision-making
• RLRs are a cost-effective approach since they require fewer resources compared to traditional literature reviews
• Offers great accessibility as RLRs provide prompt access to synthesized evidence for stakeholders
• RLRs are flexible as they can be easily adapted for various research contexts and objectives
• RLR reports are limited and restricted, not as in-depth as systematic reviews, and do not provide comprehensive coverage of the literature compared to traditional reviews.
• Susceptible to bias because of the expedited nature of RLRs. It would increase the chance of overlooking relevant studies or biases in the selection process.
• Due to time constraints, RLR findings might not be robust enough as compared to systematic reviews.

Example of a Well-Executed Rapid Literature Review

Paper Title: What Is the Impact of ChatGPT on Education? A Rapid Review of the Literature

A Summary of Literature Review Types

Tools and Resources for Conducting Different Types of Literature Reviews

Online scientific databases.

Platforms such as SciSpace , PubMed , Scopus , Elsevier , and Web of Science provide access to a vast array of scholarly literature, facilitating the search and data retrieval process.

Reference management software

Tools like SciSpace Citation Generator , EndNote, Zotero , and Mendeley assist researchers in organizing, annotating, and citing relevant literature, streamlining the review process altogether.

Automate Literature Review with AI tools

Automate the literature review process by using tools like SciSpace literature review which helps you compare and contrast multiple papers all on one screen in an easy-to-read matrix format. You can effortlessly analyze and interpret the review findings tailored to your study. It also supports the review in 75+ languages, making it more manageable even for non-English speakers.

Goes without saying — literature review plays a pivotal role in academic research to identify the current trends and provide insights to pave the way for future research endeavors. Different types of literature review has their own strengths and limitations, making them suitable for different research designs and contexts. Whether conducting a narrative review, systematic review, scoping review, integrative review, or rapid literature review, researchers must cautiously consider the objectives, resources, and the nature of the research topic.

If you’re currently working on a literature review and still adopting a manual and traditional approach, switch to the automated AI literature review workspace and transform your traditional literature review into a rapid one by extracting all the latest and relevant data for your research!

There you go!

Frequently Asked Questions

Narrative reviews give a general overview of a topic based on the author's knowledge. They may lack clear criteria and can be biased. On the other hand, systematic reviews aim to answer specific research questions by following strict methods. They're thorough but time-consuming.

A systematic review collects and analyzes existing research to provide an overview of a topic, while a meta-analysis statistically combines data from multiple studies to draw conclusions about the overall effect of an intervention or relationship between variables.

A systematic review thoroughly analyzes existing research on a specific topic using strict methods. In contrast, a scoping review offers a broader overview of the literature without evaluating individual studies in depth.

A systematic review thoroughly examines existing research using a rigorous process, while a rapid review provides a quicker summary of evidence, often by simplifying some of the systematic review steps to meet shorter timelines.

A systematic review carefully examines many studies on a single topic using specific guidelines. Conversely, an integrative review blends various types of research to provide a more comprehensive understanding of the topic.

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Systematic Reviews

• Types of Literature Reviews

What Makes a Systematic Review Different from Other Types of Reviews?

• Planning Your Systematic Review
• Database Searching
• Creating the Search
• Search Filters and Hedges
• Grey Literature
• Managing and Appraising Results
• Further Resources

Reproduced from Grant, M. J. and Booth, A. (2009), A typology of reviews: an analysis of 14 review types and associated methodologies. Health Information & Libraries Journal, 26: 91–108. doi:10.1111/j.1471-1842.2009.00848.x

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Literature Review: Types of literature reviews

• Traditional or narrative literature reviews
• Scoping Reviews
• Systematic literature reviews
• Annotated bibliography
• Keeping up to date with literature
• Finding a thesis
• Evaluating sources and critical appraisal of literature
• Managing and analysing your literature
• Further reading and resources

Types of literature reviews

The type of literature review you write will depend on your discipline and whether you are a researcher writing your PhD, publishing a study in a journal or completing an assessment task in your undergraduate study.

A literature review for a subject in an undergraduate degree will not be as comprehensive as the literature review required for a PhD thesis.

An undergraduate literature review may be in the form of an annotated bibliography or a narrative review of a small selection of literature, for example ten relevant articles. If you are asked to write a literature review, and you are an undergraduate student, be guided by your subject coordinator or lecturer.

The common types of literature reviews will be explained in the pages of this section.

• Narrative or traditional literature reviews
• Critically Appraised Topic (CAT)
• Scoping reviews
• Annotated bibliographies

These are not the only types of reviews of literature that can be conducted. Often the term "review" and "literature" can be confusing and used in the wrong context. Grant and Booth (2009) attempt to clear up this confusion by discussing 14 review types and the associated methodology, and advantages and disadvantages associated with each review.

Grant, M. J. and Booth, A. (2009), A typology of reviews: an analysis of 14 review types and associated methodologies . Health Information & Libraries Journal, 26 , 91–108. doi:10.1111/j.1471-1842.2009.00848.x

What's the difference between reviews?

Researchers, academics, and librarians all use various terms to describe different types of literature reviews, and there is often inconsistency in the ways the types are discussed. Here are a couple of simple explanations.

• The image below describes common review types in terms of speed, detail, risk of bias, and comprehensiveness:

"Schematic of the main differences between the types of literature review" by Brennan, M. L., Arlt, S. P., Belshaw, Z., Buckley, L., Corah, L., Doit, H., Fajt, V. R., Grindlay, D., Moberly, H. K., Morrow, L. D., Stavisky, J., & White, C. (2020). Critically Appraised Topics (CATs) in veterinary medicine: Applying evidence in clinical practice. Frontiers in Veterinary Science, 7 , 314. https://doi.org/10.3389/fvets.2020.00314 is licensed under CC BY 3.0

• The table below lists four of the most common types of review , as adapted from a widely used typology of fourteen types of reviews (Grant & Booth, 2009).  

Grant, M.J. & Booth, A. (2009).  A typology of reviews: An analysis of 14 review types and associated methodologies. Health Information & Libraries Journal, 26 (2), 91-108. https://doi.org/10.1111/j.1471-1842.2009.00848.x

See also the Library's  Literature Review guide.

Critical Appraised Topic (CAT)

For information on conducting a Critically Appraised Topic or CAT

Callander, J., Anstey, A. V., Ingram, J. R., Limpens, J., Flohr, C., & Spuls, P. I. (2017).  How to write a Critically Appraised Topic: evidence to underpin routine clinical practice.  British Journal of Dermatology (1951), 177(4), 1007-1013. https://doi.org/10.1111/bjd.15873 

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• How to Write a Literature Review | Guide, Examples, & Templates

How to Write a Literature Review | Guide, Examples, & Templates

Published on January 2, 2023 by Shona McCombes . Revised on September 11, 2023.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research that you can later apply to your paper, thesis, or dissertation topic .

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates, and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarize sources—it analyzes, synthesizes , and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

What is the purpose of a literature review, examples of literature reviews, step 1 – search for relevant literature, step 2 – evaluate and select sources, step 3 – identify themes, debates, and gaps, step 4 – outline your literature review’s structure, step 5 – write your literature review, free lecture slides, other interesting articles, frequently asked questions, introduction.

• Quick Run-through
• Step 1 & 2

When you write a thesis , dissertation , or research paper , you will likely have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and its scholarly context
• Develop a theoretical framework and methodology for your research
• Position your work in relation to other researchers and theorists
• Show how your research addresses a gap or contributes to a debate
• Evaluate the current state of research and demonstrate your knowledge of the scholarly debates around your topic.

Writing literature reviews is a particularly important skill if you want to apply for graduate school or pursue a career in research. We’ve written a step-by-step guide that you can follow below.

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See an example

Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research problem and questions .

Make a list of keywords

Start by creating a list of keywords related to your research question. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list as you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some useful databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can also use boolean operators to help narrow down your search.

Make sure to read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

You likely won’t be able to read absolutely everything that has been written on your topic, so it will be necessary to evaluate which sources are most relevant to your research question.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models, and methods?
• Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible , and make sure you read any landmark studies and major theories in your field of research.

You can use our template to summarize and evaluate sources you’re thinking about using. Click on either button below to download.

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It is important to keep track of your sources with citations to avoid plagiarism . It can be helpful to make an annotated bibliography , where you compile full citation information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

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To begin organizing your literature review’s argument and structure, be sure you understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly visual platforms like Instagram and Snapchat—this is a gap that you could address in your own research.

There are various approaches to organizing the body of a literature review. Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarizing sources in order.

Try to analyze patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organize your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text , your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, you can follow these tips:

• Summarize and synthesize: give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: don’t just paraphrase other researchers — add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically evaluate: mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: use transition words and topic sentences to draw connections, comparisons and contrasts

In the conclusion, you should summarize the key findings you have taken from the literature and emphasize their significance.

When you’ve finished writing and revising your literature review, don’t forget to proofread thoroughly before submitting. Not a language expert? Check out Scribbr’s professional proofreading services !

This article has been adapted into lecture slides that you can use to teach your students about writing a literature review.

Scribbr slides are free to use, customize, and distribute for educational purposes.

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If you want to know more about the research process , methodology , research bias , or statistics , make sure to check out some of our other articles with explanations and examples.

• Sampling methods
• Simple random sampling
• Stratified sampling
• Cluster sampling
• Likert scales
• Reproducibility

 Statistics

• Null hypothesis
• Statistical power
• Probability distribution
• Effect size
• Poisson distribution

Research bias

• Optimism bias
• Cognitive bias
• Implicit bias
• Hawthorne effect
• Anchoring bias
• Explicit bias

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a thesis, dissertation , or research paper , in order to situate your work in relation to existing knowledge.

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarize yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your thesis or dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

A literature review is a survey of credible sources on a topic, often used in dissertations , theses, and research papers . Literature reviews give an overview of knowledge on a subject, helping you identify relevant theories and methods, as well as gaps in existing research. Literature reviews are set up similarly to other  academic texts , with an introduction , a main body, and a conclusion .

An  annotated bibliography is a list of  source references that has a short description (called an annotation ) for each of the sources. It is often assigned as part of the research process for a  paper .  

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Literature Reviews

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Literature Reviews within a Scholarly Work

Literature reviews as a scholarly work.

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Literature reviews summarize and analyze what has been written on a particular topic and identify gaps or disagreements in the scholarly work on that topic.

Within a scholarly work, the literature review situates the current work within the larger scholarly conversation and emphasizes how that particular scholarly work contributes to the conversation on the topic. The literature review portion may be as brief as a few paragraphs focusing on a narrow topic area.

When writing this type of literature review, it's helpful to start by identifying sources most relevant to your research question. A citation tracking database such as Web of Science can also help you locate seminal articles on a topic and find out who has more recently cited them. See "Your Literature Search" for more details.

A literature review may itself be a scholarly publication and provide an analysis of what has been written on a particular topic without contributing original research. These types of literature reviews can serve to help keep people updated on a field as well as helping scholars choose a research topic to fill gaps in the knowledge on that topic. Common types include:

Systematic Review

Systematic literature reviews follow specific procedures in some ways similar to setting up an experiment to ensure that future scholars can replicate the same steps. They are also helpful for evaluating data published over multiple studies. Thus, these are common in the medical field and may be used by healthcare providers to help guide diagnosis and treatment decisions. Cochrane Reviews are one example of this type of literature review.

Semi-Systematic Review

When a systematic review is not feasible, a semi-systematic review can help synthesize research on a topic or how a topic has been studied in different fields (Snyder 2019). Rather than focusing on quantitative data, this review type identifies themes, theoretical perspectives, and other qualitative information related to the topic. These types of reviews can be particularly helpful for a historical topic overview, for developing a theoretical model, and for creating a research agenda for a field (Snyder 2019). As with systematic reviews, a search strategy must be developed before conducting the review.

Integrative Review

An integrative review is less systematic and can be helpful for developing a theoretical model or to reconceptualize a topic. As Synder (2019) notes, " This type of review often re quires a more creative collection of data, as the purpose is usually not to cover all articles ever published on the topic but rather to combine perspectives and insights from di ff erent fi elds or research traditions" (p. 336).

Source: Snyder, H. (2019). Literature review as a research methodology: An overview and guidelines. Journal of Business Research. 104. 333-339. doi: 10.1016/j.jbusres.2019.07.039

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Writing a Literature Review

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

• An introductory paragraph that explains what your working topic and thesis is
• A forecast of key topics or texts that will appear in the review
• Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
• Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically Evaluate: Mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

• Summarize the key findings you have taken from the literature and emphasize their significance
• Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

• Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
• Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
• Qualitative versus quantitative research
• Empirical versus theoretical scholarship
• Divide the research by sociological, historical, or cultural sources
• Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

• It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
• Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
• Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
• Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

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Evidence Synthesis, Systematic Review Services : Literature Review Types, Taxonomies

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Choosing a Literature Review Methodology

Growing interest in evidence-based practice has driven an increase in review methodologies. Your choice of review methodology (or literature review type) will be informed by the intent (purpose, function) of your research project and the time and resources of your team. 

• Decision Tree (What Type of Review is Right for You?) Developed by Cornell University Library staff, this "decision-tree" guides the user to a handful of review guides given time and intent.

Types of Evidence Synthesis*

Critical Review - Aims to demonstrate writer has extensively researched literature and critically evaluated its quality. Goes beyond mere description to include degree of analysis and conceptual innovation. Typically results in hypothesis or model.

Mapping Review (Systematic Map) - Map out and categorize existing literature from which to commission further reviews and/or primary research by identifying gaps in research literature.

Meta-Analysis - Technique that statistically combines the results of quantitative studies to provide a more precise effect of the results.

Mixed Studies Review (Mixed Methods Review) - Refers to any combination of methods where one significant component is a literature review (usually systematic). Within a review context it refers to a combination of review approaches for example combining quantitative with qualitative research or outcome with process studies.

Narrative (Literature) Review - Generic term: published materials that provide examination of recent or current literature. Can cover wide range of subjects at various levels of completeness and comprehensiveness.

Overview - Generic term: summary of the [medical] literature that attempts to survey the literature and describe its characteristics.

Qualitative Systematic Review or Qualitative Evidence Synthesis - Method for integrating or comparing the findings from qualitative studies. It looks for ‘themes’ or ‘constructs’ that lie in or across individual qualitative studies.

Rapid Review - Assessment of what is already known about a policy or practice issue, by using systematic review methods to search and critically appraise existing research.

Scoping Review or Evidence Map - Preliminary assessment of potential size and scope of available research literature. Aims to identify nature and extent of research.

State-of-the-art Review - Tend to address more current matters in contrast to other combined retrospective and current approaches. May offer new perspectives on issue or point out area for further research.

Systematic Review - Seeks to systematically search for, appraise and synthesis research evidence, often adhering to guidelines on the conduct of a review. (An emerging subset includes Living Reviews or Living Systematic Reviews - A [review or] systematic review which is continually updated, incorporating relevant new evidence as it becomes available.)

Systematic Search and Review - Combines strengths of critical review with a comprehensive search process. Typically addresses broad questions to produce ‘best evidence synthesis.’

Umbrella Review - Specifically refers to review compiling evidence from multiple reviews into one accessible and usable document. Focuses on broad condition or problem for which there are competing interventions and highlights reviews that address these interventions and their results.

*These definitions are in Grant & Booth's "A Typology of Reviews: An Analysis of 14 Review Types and Associated Methodologies."

Literature Review Types/Typologies, Taxonomies

Grant, M. J., and A. Booth. "A Typology of Reviews: An Analysis of 14 Review Types and Associated Methodologies."  Health Information and Libraries Journal  26.2 (2009): 91-108.  DOI: 10.1111/j.1471-1842.2009.00848.x  Link

Munn, Zachary, et al. “Systematic Review or Scoping Review? Guidance for Authors When Choosing between a Systematic or Scoping Review Approach.” BMC Medical Research Methodology , vol. 18, no. 1, Nov. 2018, p. 143. DOI: 10.1186/s12874-018-0611-x. Link

Sutton, A., et al. "Meeting the Review Family: Exploring Review Types and Associated Information Retrieval Requirements."  Health Information and Libraries Journal  36.3 (2019): 202-22.  DOI: 10.1111/hir.12276  Link

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Literature Reviews

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Types of reviews and examples

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• 2. Plan your search
• 3. Search the literature
• 4. Organize your results
• 5. Synthesize your findings
• 6. Write the review
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• Meta-analysis
• Systematized

Definition:

"A term used to describe a conventional overview of the literature, particularly when contrasted with a systematic review (Booth et al., 2012, p. 265).

Characteristics:

• Provides examination of recent or current literature on a wide range of subjects
• Varying levels of completeness / comprehensiveness, non-standardized methodology
• May or may not include comprehensive searching, quality assessment or critical appraisal

Mitchell, L. E., & Zajchowski, C. A. (2022). The history of air quality in Utah: A narrative review.  Sustainability ,  14 (15), 9653.  doi.org/10.3390/su14159653

Booth, A., Papaioannou, D., & Sutton, A. (2012). Systematic approaches to a successful literature review. London: SAGE Publications Ltd.

"An assessment of what is already known about a policy or practice issue...using systematic review methods to search and critically appraise existing research" (Grant & Booth, 2009, p. 100).

• Assessment of what is already known about an issue
• Similar to a systematic review but within a time-constrained setting
• Typically employs methodological shortcuts, increasing risk of introducing bias, includes basic level of quality assessment
• Best suited for issues needing quick decisions and solutions (i.e., policy recommendations)

Learn more about the method:

Khangura, S., Konnyu, K., Cushman, R., Grimshaw, J., & Moher, D. (2012). Evidence summaries: the evolution of a rapid review approach.  Systematic reviews, 1 (1), 1-9.  https://doi.org/10.1186/2046-4053-1-10

Virginia Commonwealth University Libraries. (2021). Rapid Review Protocol .

Quarmby, S., Santos, G., & Mathias, M. (2019). Air quality strategies and technologies: A rapid review of the international evidence.  Sustainability, 11 (10), 2757.  https://doi.org/10.3390/su11102757

Grant, M.J. & Booth, A. (2009). A typology of reviews: an analysis of the 14 review types and associated methodologies.  Health Information & Libraries Journal , 26(2), 91-108. https://www.doi.org/10.1111/j.1471-1842.2009.00848.x

Developed and refined by the Evidence for Policy and Practice Information and Co-ordinating Centre (EPPI-Centre), this review "map[s] out and categorize[s] existing literature on a particular topic, identifying gaps in research literature from which to commission further reviews and/or primary research" (Grant & Booth, 2009, p. 97).

Although mapping reviews are sometimes called scoping reviews, the key difference is that mapping reviews focus on a review question, rather than a topic

Mapping reviews are "best used where a clear target for a more focused evidence product has not yet been identified" (Booth, 2016, p. 14)

Mapping review searches are often quick and are intended to provide a broad overview

Mapping reviews can take different approaches in what types of literature is focused on in the search

Cooper I. D. (2016). What is a "mapping study?".  Journal of the Medical Library Association: JMLA ,  104 (1), 76–78. https://doi.org/10.3163/1536-5050.104.1.013

Miake-Lye, I. M., Hempel, S., Shanman, R., & Shekelle, P. G. (2016). What is an evidence map? A systematic review of published evidence maps and their definitions, methods, and products.  Systematic reviews, 5 (1), 1-21.  https://doi.org/10.1186/s13643-016-0204-x

Tainio, M., Andersen, Z. J., Nieuwenhuijsen, M. J., Hu, L., De Nazelle, A., An, R., ... & de Sá, T. H. (2021). Air pollution, physical activity and health: A mapping review of the evidence.  Environment international ,  147 , 105954.  https://doi.org/10.1016/j.envint.2020.105954

Booth, A. (2016). EVIDENT Guidance for Reviewing the Evidence: a compendium of methodological literature and websites . ResearchGate. https://doi.org/10.13140/RG.2.1.1562.9842 . 

Grant, M.J. & Booth, A. (2009). A typology of reviews: an analysis of the 14 review types and associated methodologies.  Health Information & Libraries Journal , 26(2), 91-108.  https://www.doi.org/10.1111/j.1471-1842.2009.00848.x

"A type of review that has as its primary objective the identification of the size and quality of research in a topic area in order to inform subsequent review" (Booth et al., 2012, p. 269).

• Main purpose is to map out and categorize existing literature, identify gaps in literature—great for informing policy-making
• Search comprehensiveness determined by time/scope constraints, could take longer than a systematic review
• No formal quality assessment or critical appraisal

Learn more about the methods :

Arksey, H., & O'Malley, L. (2005) Scoping studies: towards a methodological framework.  International Journal of Social Research Methodology ,  8 (1), 19-32.  https://doi.org/10.1080/1364557032000119616

Levac, D., Colquhoun, H., & O’Brien, K. K. (2010). Scoping studies: Advancing the methodology. Implementation Science: IS, 5, 69. https://doi.org/10.1186/1748-5908-5-69

Example : 

Rahman, A., Sarkar, A., Yadav, O. P., Achari, G., & Slobodnik, J. (2021). Potential human health risks due to environmental exposure to nano-and microplastics and knowledge gaps: A scoping review.  Science of the Total Environment, 757 , 143872.  https://doi.org/10.1016/j.scitotenv.2020.143872

A review that "[compiles] evidence from multiple...reviews into one accessible and usable document" (Grant & Booth, 2009, p. 103). While originally intended to be a compilation of Cochrane reviews, it now generally refers to any kind of evidence synthesis.

• Compiles evidence from multiple reviews into one document
• Often defines a broader question than is typical of a traditional systematic review

Choi, G. J., & Kang, H. (2022). The umbrella review: a useful strategy in the rain of evidence.  The Korean Journal of Pain ,  35 (2), 127–128.  https://doi.org/10.3344/kjp.2022.35.2.127

Aromataris, E., Fernandez, R., Godfrey, C. M., Holly, C., Khalil, H., & Tungpunkom, P. (2015). Summarizing systematic reviews: Methodological development, conduct and reporting of an umbrella review approach. International Journal of Evidence-Based Healthcare , 13(3), 132–140. https://doi.org/10.1097/XEB.0000000000000055

Rojas-Rueda, D., Morales-Zamora, E., Alsufyani, W. A., Herbst, C. H., Al Balawi, S. M., Alsukait, R., & Alomran, M. (2021). Environmental risk factors and health: An umbrella review of meta-analyses.  International Journal of Environmental Research and Public Dealth ,  18 (2), 704.  https://doi.org/10.3390/ijerph18020704

A meta-analysis is a "technique that statistically combines the results of quantitative studies to provide a more precise effect of the result" (Grant & Booth, 2009, p. 98).

• Statistical technique for combining results of quantitative studies to provide more precise effect of results
• Aims for exhaustive, comprehensive searching
• Quality assessment may determine inclusion/exclusion criteria
• May be conducted independently or as part of a systematic review

Berman, N. G., & Parker, R. A. (2002). Meta-analysis: Neither quick nor easy. BMC Medical Research Methodology , 2(1), 10. https://doi.org/10.1186/1471-2288-2-10

Hites R. A. (2004). Polybrominated diphenyl ethers in the environment and in people: a meta-analysis of concentrations.  Environmental Science & Technology ,  38 (4), 945–956.  https://doi.org/10.1021/es035082g

A systematic review "seeks to systematically search for, appraise, and [synthesize] research evidence, often adhering to the guidelines on the conduct of a review" provided by discipline-specific organizations, such as the Cochrane Collaboration (Grant & Booth, 2009, p. 102).

• Aims to compile and synthesize all known knowledge on a given topic
• Adheres to strict guidelines, protocols, and frameworks
• Time-intensive and often takes months to a year or more to complete
• The most commonly referred to type of evidence synthesis. Sometimes confused as a blanket term for other types of reviews

Gascon, M., Triguero-Mas, M., Martínez, D., Dadvand, P., Forns, J., Plasència, A., & Nieuwenhuijsen, M. J. (2015). Mental health benefits of long-term exposure to residential green and blue spaces: a systematic review.  International Journal of Environmental Research and Public Health ,  12 (4), 4354–4379.  https://doi.org/10.3390/ijerph120404354

"Systematized reviews attempt to include one or more elements of the systematic review process while stopping short of claiming that the resultant output is a systematic review" (Grant & Booth, 2009, p. 102). When a systematic review approach is adapted to produce a more manageable scope, while still retaining the rigor of a systematic review such as risk of bias assessment and the use of a protocol, this is often referred to as a  structured review  (Huelin et al., 2015).

• Typically conducted by postgraduate or graduate students
• Often assigned by instructors to students who don't have the resources to conduct a full systematic review

Salvo, G., Lashewicz, B. M., Doyle-Baker, P. K., & McCormack, G. R. (2018). Neighbourhood built environment influences on physical activity among adults: A systematized review of qualitative evidence.  International Journal of Environmental Research and Public Health ,  15 (5), 897.  https://doi.org/10.3390/ijerph15050897

Huelin, R., Iheanacho, I., Payne, K., & Sandman, K. (2015). What’s in a name? Systematic and non-systematic literature reviews, and why the distinction matters. https://www.evidera.com/resource/whats-in-a-name-systematic-and-non-systematic-literature-reviews-and-why-the-distinction-matters/

• Review Decision Tree - Cornell University For more information, check out Cornell's review methodology decision tree.
• LitR-Ex.com - Eight literature review methodologies Learn more about 8 different review types (incl. Systematic Reviews and Scoping Reviews) with practical tips about strengths and weaknesses of different methods.
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Literature reviews, what is a literature review, learning more about how to do a literature review.

• Planning the Review
• The Research Question
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• Writing the Review

A literature review is a review and synthesis of existing research on a topic or research question. A literature review is meant to analyze the scholarly literature, make connections across writings and identify strengths, weaknesses, trends, and missing conversations. A literature review should address different aspects of a topic as it relates to your research question. A literature review goes beyond a description or summary of the literature you have read. 

• Sage Research Methods Core This link opens in a new window SAGE Research Methods supports research at all levels by providing material to guide users through every step of the research process. SAGE Research Methods is the ultimate methods library with more than 1000 books, reference works, journal articles, and instructional videos by world-leading academics from across the social sciences, including the largest collection of qualitative methods books available online from any scholarly publisher. – Publisher

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Literature Reviews

• Getting Started

Selecting a Review Type

Defining the scope of your review, four common types of reviews.

• Developing a Research Question
• Searching the Literature
• Searching Tips
• ChatGPT [beta]
• Documenting your Search
• Using Citation Managers
• Concept Mapping
• Writing the Review
• Further Resources

More Review Types

This article by Sutton & Booth (2019) explores 48 distinct types of Literature Reviews:

Which Review is Right for You?

The  Right Review tool  has questions about your lit review process and plans. It offers a qualitative and quantitative option. At completion, you are given a lit review type recommendation.

You'll want to think about the kind of review you are doing. Is it a selective or comprehensive review? Is the review part of a larger work or a stand-alone work ?

For example, if you're writing the Literature Review section of a journal article, that's a selective review which is part of a larger work. Alternatively, if you're writing a review article, that's a comprehensive review which is a stand-alone work. Thinking about this will help you develop the scope of the review.

This exercise will help define the scope of your Literature Review, setting the boundaries for which literature to include and which to exclude.

A FEW GENERAL CONSIDERATIONS WHEN DEFINING SCOPE

• Which populations to investigate — this can include gender, age, socio-economic status, race, geographic location, etc., if the research area includes humans.
• What years to include — if researching the legalization of medicinal cannabis, you might only look at the previous 20 years; but if researching dolphin mating practices, you might extend many more decades.
• Which subject areas — if researching artificial intelligence, subject areas could be computer science, robotics, or health sciences
• How many sources  — a selective review for a class assignment might only need ten, while a comprehensive review for a dissertation might include hundreds. There is no one right answer.
• There will be many other considerations that are more specific to your topic. 

Most databases will allow you to limit years and subject areas, so look for those tools while searching. See the Searching Tips tab for information on how use these tools.

LITERATURE REVIEW

• Often used as a generic term to describe any type of review
• More precise definition:  Published materials that provide an examination of published literature . Can cover wide range of subjects at various levels of comprehensiveness.
• Identifies gaps in research, explains importance of topic, hypothesizes future work, etc.
• Usually written as part of a larger work like a journal article or dissertation

SCOPING REVIEW

• Conducted to address broad research questions with the goal of understanding the extent of research that has been conducted.
• Provides a preliminary assessment of the potential size and scope of available research literature. It aims to identify the nature and extent of research evidence (usually including ongoing research) 
• Doesn't assess the quality of the literature gathered (i.e. presence of literature on a topic shouldn’t be conflated w/ the quality of that literature)
• " Preparing scoping reviews for publication using methodological guides and reporting standards " is a great article to read on Scoping Reviews

SYSTEMATIC REVIEW

• Common in the health sciences ( Taubman Health Sciences Library guide to Systematic Reviews )
• Goal: collect all literature that meets specific criteria (methodology, population, treatment, etc.) and then appraise its quality and synthesize it
• Follows strict protocol for literature collection, appraisal and synthesis
• Typically performed by research teams 
• Takes 12-18 months to complete
• Often written as a stand alone work

META-ANALYSIS

• Goes one step further than a systematic review by statistically combining the results of quantitative studies to provide a more precise effect of the results. 
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• UConn Library
• Literature Review: The What, Why and How-to Guide
• Introduction

Literature Review: The What, Why and How-to Guide — Introduction

• Getting Started
• How to Pick a Topic
• Strategies to Find Sources
• Evaluating Sources & Lit. Reviews
• Tips for Writing Literature Reviews
• Writing Literature Review: Useful Sites
• Citation Resources
• Other Academic Writings

What are Literature Reviews?

So, what is a literature review? "A literature review is an account of what has been published on a topic by accredited scholars and researchers. In writing the literature review, your purpose is to convey to your reader what knowledge and ideas have been established on a topic, and what their strengths and weaknesses are. As a piece of writing, the literature review must be defined by a guiding concept (e.g., your research objective, the problem or issue you are discussing, or your argumentative thesis). It is not just a descriptive list of the material available, or a set of summaries." Taylor, D.  The literature review: A few tips on conducting it . University of Toronto Health Sciences Writing Centre.

Goals of Literature Reviews

What are the goals of creating a Literature Review?  A literature could be written to accomplish different aims:

• To develop a theory or evaluate an existing theory
• To summarize the historical or existing state of a research topic
• Identify a problem in a field of research 

Baumeister, R. F., & Leary, M. R. (1997). Writing narrative literature reviews .  Review of General Psychology , 1 (3), 311-320.

What kinds of sources require a Literature Review?

• A research paper assigned in a course
• A thesis or dissertation
• A grant proposal
• An article intended for publication in a journal

All these instances require you to collect what has been written about your research topic so that you can demonstrate how your own research sheds new light on the topic.

Types of Literature Reviews

What kinds of literature reviews are written?

Narrative review: The purpose of this type of review is to describe the current state of the research on a specific topic/research and to offer a critical analysis of the literature reviewed. Studies are grouped by research/theoretical categories, and themes and trends, strengths and weakness, and gaps are identified. The review ends with a conclusion section which summarizes the findings regarding the state of the research of the specific study, the gaps identify and if applicable, explains how the author's research will address gaps identify in the review and expand the knowledge on the topic reviewed.

• Example : Predictors and Outcomes of U.S. Quality Maternity Leave: A Review and Conceptual Framework:  10.1177/08948453211037398  

Systematic review : "The authors of a systematic review use a specific procedure to search the research literature, select the studies to include in their review, and critically evaluate the studies they find." (p. 139). Nelson, L. K. (2013). Research in Communication Sciences and Disorders . Plural Publishing.

• Example : The effect of leave policies on increasing fertility: a systematic review:  10.1057/s41599-022-01270-w

Meta-analysis : "Meta-analysis is a method of reviewing research findings in a quantitative fashion by transforming the data from individual studies into what is called an effect size and then pooling and analyzing this information. The basic goal in meta-analysis is to explain why different outcomes have occurred in different studies." (p. 197). Roberts, M. C., & Ilardi, S. S. (2003). Handbook of Research Methods in Clinical Psychology . Blackwell Publishing.

• Example : Employment Instability and Fertility in Europe: A Meta-Analysis:  10.1215/00703370-9164737

Meta-synthesis : "Qualitative meta-synthesis is a type of qualitative study that uses as data the findings from other qualitative studies linked by the same or related topic." (p.312). Zimmer, L. (2006). Qualitative meta-synthesis: A question of dialoguing with texts .  Journal of Advanced Nursing , 53 (3), 311-318.

• Example : Women’s perspectives on career successes and barriers: A qualitative meta-synthesis:  10.1177/05390184221113735

Literature Reviews in the Health Sciences

• UConn Health subject guide on systematic reviews Explanation of the different review types used in health sciences literature as well as tools to help you find the right review type
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Literature Review: Types of Literature Reviews

• Literature Review
• Purpose of a Literature Review
• Work in Progress
• Compiling & Writing
• Books, Articles, & Web Pages

Types of Literature Reviews

• Departmental Differences
• Citation Styles & Plagiarism
• Know the Difference! Systematic Review vs. Literature Review

It is important to think of knowledge in a given field as consisting of three layers.

• First, there are the primary studies that researchers conduct and publish.
• Second, are the reviews of those studies that summarize and offer new interpretations built from and often extending beyond the original studies.
• Third, there are the perceptions, conclusions, opinions, and interpretations that are shared informally that become part of the lore of the field.

In composing a literature review, it is important to note that it is often this third layer of knowledge that is cited as "true" even though it often has only a loose relationship to the primary studies and secondary literature reviews.

Given this, while literature reviews are designed to provide an overview and synthesis of pertinent sources you have explored, there are several approaches to how they can be done, depending upon the type of analysis underpinning your study. Listed below are definitions of types of literature reviews:

Argumentative Review      This form examines literature selectively in order to support or refute an argument, deeply embedded assumption, or philosophical problem already established in the literature. The purpose is to develop a body of literature that establishes a contrarian viewpoint. Given the value-laden nature of some social science research [e.g., educational reform; immigration control], argumentative approaches to analyzing the literature can be a legitimate and important form of discourse. However, note that they can also introduce problems of bias when they are used to make summary claims of the sort found in systematic reviews.

Integrative Review      Considered a form of research that reviews, critiques, and synthesizes representative literature on a topic in an integrated way such that new frameworks and perspectives on the topic are generated. The body of literature includes all studies that address related or identical hypotheses. A well-done integrative review meets the same standards as primary research in regard to clarity, rigor, and replication.

Historical Review      Few things rest in isolation from historical precedent. Historical reviews are focused on examining research throughout a period of time, often starting with the first time an issue, concept, theory, phenomenon emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and to identify the likely directions for future research.

Methodological Review      A review does not always focus on what someone said [content], but how they said it [method of analysis]. This approach provides a framework of understanding at different levels (i.e. those of theory, substantive fields, research approaches, and data collection and analysis techniques), enables researchers to draw on a wide variety of knowledge ranging from the conceptual level to practical documents for use in fieldwork in the areas of ontological and epistemological consideration, quantitative and qualitative integration, sampling, interviewing, data collection and data analysis, and helps highlight many ethical issues which we should be aware of and consider as we go through our study.

Systematic Review      This form consists of an overview of existing evidence pertinent to a clearly formulated research question, which uses pre-specified and standardized methods to identify and critically appraise relevant research, and to collect, report, and analyze data from the studies that are included in the review. Typically it focuses on a very specific empirical question, often posed in a cause-and-effect form, such as "To what extent does A contribute to B?"

Theoretical Review      The purpose of this form is to concretely examine the corpus of theory that has accumulated in regard to an issue, concept, theory, phenomenon. The theoretical literature review help establish what theories already exist, the relationships between them, to what degree the existing theories have been investigated, and to develop new hypotheses to be tested. Often this form is used to help establish a lack of appropriate theories or reveal that current theories are inadequate for explaining new or emerging research problems. The unit of analysis can focus on a theoretical concept or a whole theory or framework.

* Kennedy, Mary M. "Defining a Literature." Educational Researcher 36 (April 2007): 139-147.

All content is from The Literature Review created by Dr. Robert Larabee USC

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Harvey Cushing/John Hay Whitney Medical Library

• Collections
• Research Help

YSN Doctoral Programs: Steps in Conducting a Literature Review

• Biomedical Databases
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• Soc. Sci., History, and Law Databases
• Grey Literature
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• Google Tips
• Recommended Books
• Steps in Conducting a Literature Review

What is a literature review?

A literature review is an integrated analysis -- not just a summary-- of scholarly writings and other relevant evidence related directly to your research question.  That is, it represents a synthesis of the evidence that provides background information on your topic and shows a association between the evidence and your research question.

A literature review may be a stand alone work or the introduction to a larger research paper, depending on the assignment.  Rely heavily on the guidelines your instructor has given you.

Why is it important?

A literature review is important because it:

• Explains the background of research on a topic.
• Demonstrates why a topic is significant to a subject area.
• Discovers relationships between research studies/ideas.
• Identifies major themes, concepts, and researchers on a topic.
• Identifies critical gaps and points of disagreement.
• Discusses further research questions that logically come out of the previous studies.

APA7 Style resources

APA Style Blog - for those harder to find answers

1. Choose a topic. Define your research question.

Your literature review should be guided by your central research question.  The literature represents background and research developments related to a specific research question, interpreted and analyzed by you in a synthesized way.

• Make sure your research question is not too broad or too narrow.  Is it manageable?
• Begin writing down terms that are related to your question. These will be useful for searches later.
• If you have the opportunity, discuss your topic with your professor and your class mates.

2. Decide on the scope of your review

How many studies do you need to look at? How comprehensive should it be? How many years should it cover? 

• This may depend on your assignment.  How many sources does the assignment require?

3. Select the databases you will use to conduct your searches.

Make a list of the databases you will search. 

Where to find databases:

• use the tabs on this guide
• Find other databases in the Nursing Information Resources web page
• More on the Medical Library web page
• ... and more on the Yale University Library web page

4. Conduct your searches to find the evidence. Keep track of your searches.

• Use the key words in your question, as well as synonyms for those words, as terms in your search. Use the database tutorials for help.
• Save the searches in the databases. This saves time when you want to redo, or modify, the searches. It is also helpful to use as a guide is the searches are not finding any useful results.
• Review the abstracts of research studies carefully. This will save you time.
• Use the bibliographies and references of research studies you find to locate others.
• Check with your professor, or a subject expert in the field, if you are missing any key works in the field.
• Ask your librarian for help at any time.
• Use a citation manager, such as EndNote as the repository for your citations. See the EndNote tutorials for help.

Review the literature

Some questions to help you analyze the research:

• What was the research question of the study you are reviewing? What were the authors trying to discover?
• Was the research funded by a source that could influence the findings?
• What were the research methodologies? Analyze its literature review, the samples and variables used, the results, and the conclusions.
• Does the research seem to be complete? Could it have been conducted more soundly? What further questions does it raise?
• If there are conflicting studies, why do you think that is?
• How are the authors viewed in the field? Has this study been cited? If so, how has it been analyzed?

Tips: 

• Review the abstracts carefully.  
• Keep careful notes so that you may track your thought processes during the research process.
• Create a matrix of the studies for easy analysis, and synthesis, across all of the studies.
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What Is A Literature Review?

A plain-language explainer (with examples).

By:  Derek Jansen (MBA) & Kerryn Warren (PhD) | June 2020 (Updated May 2023)

If you’re faced with writing a dissertation or thesis, chances are you’ve encountered the term “literature review” . If you’re on this page, you’re probably not 100% what the literature review is all about. The good news is that you’ve come to the right place.

Literature Review 101

• What (exactly) is a literature review
• What’s the purpose of the literature review chapter
• How to find high-quality resources
• How to structure your literature review chapter
• Example of an actual literature review

What is a literature review?

The word “literature review” can refer to two related things that are part of the broader literature review process. The first is the task of  reviewing the literature  – i.e. sourcing and reading through the existing research relating to your research topic. The second is the  actual chapter  that you write up in your dissertation, thesis or research project. Let’s look at each of them:

Reviewing the literature

The first step of any literature review is to hunt down and  read through the existing research  that’s relevant to your research topic. To do this, you’ll use a combination of tools (we’ll discuss some of these later) to find journal articles, books, ebooks, research reports, dissertations, theses and any other credible sources of information that relate to your topic. You’ll then  summarise and catalogue these  for easy reference when you write up your literature review chapter. 

The literature review chapter

The second step of the literature review is to write the actual literature review chapter (this is usually the second chapter in a typical dissertation or thesis structure ). At the simplest level, the literature review chapter is an  overview of the key literature  that’s relevant to your research topic. This chapter should provide a smooth-flowing discussion of what research has already been done, what is known, what is unknown and what is contested in relation to your research topic. So, you can think of it as an  integrated review of the state of knowledge  around your research topic. 

What’s the purpose of a literature review?

The literature review chapter has a few important functions within your dissertation, thesis or research project. Let’s take a look at these:

Purpose #1 – Demonstrate your topic knowledge

The first function of the literature review chapter is, quite simply, to show the reader (or marker) that you  know what you’re talking about . In other words, a good literature review chapter demonstrates that you’ve read the relevant existing research and understand what’s going on – who’s said what, what’s agreed upon, disagreed upon and so on. This needs to be  more than just a summary  of who said what – it needs to integrate the existing research to  show how it all fits together  and what’s missing (which leads us to purpose #2, next). 

Purpose #2 – Reveal the research gap that you’ll fill

The second function of the literature review chapter is to  show what’s currently missing  from the existing research, to lay the foundation for your own research topic. In other words, your literature review chapter needs to show that there are currently “missing pieces” in terms of the bigger puzzle, and that  your study will fill one of those research gaps . By doing this, you are showing that your research topic is original and will help contribute to the body of knowledge. In other words, the literature review helps justify your research topic.  

Purpose #3 – Lay the foundation for your conceptual framework

The third function of the literature review is to form the  basis for a conceptual framework . Not every research topic will necessarily have a conceptual framework, but if your topic does require one, it needs to be rooted in your literature review. 

For example, let’s say your research aims to identify the drivers of a certain outcome – the factors which contribute to burnout in office workers. In this case, you’d likely develop a conceptual framework which details the potential factors (e.g. long hours, excessive stress, etc), as well as the outcome (burnout). Those factors would need to emerge from the literature review chapter – they can’t just come from your gut! 

So, in this case, the literature review chapter would uncover each of the potential factors (based on previous studies about burnout), which would then be modelled into a framework. 

Purpose #4 – To inform your methodology

The fourth function of the literature review is to  inform the choice of methodology  for your own research. As we’ve  discussed on the Grad Coach blog , your choice of methodology will be heavily influenced by your research aims, objectives and questions . Given that you’ll be reviewing studies covering a topic close to yours, it makes sense that you could learn a lot from their (well-considered) methodologies.

So, when you’re reviewing the literature, you’ll need to  pay close attention to the research design , methodology and methods used in similar studies, and use these to inform your methodology. Quite often, you’ll be able to  “borrow” from previous studies . This is especially true for quantitative studies , as you can use previously tried and tested measures and scales. 

How do I find articles for my literature review?

Finding quality journal articles is essential to crafting a rock-solid literature review. As you probably already know, not all research is created equally, and so you need to make sure that your literature review is  built on credible research . 

We could write an entire post on how to find quality literature (actually, we have ), but a good starting point is Google Scholar . Google Scholar is essentially the academic equivalent of Google, using Google’s powerful search capabilities to find relevant journal articles and reports. It certainly doesn’t cover every possible resource, but it’s a very useful way to get started on your literature review journey, as it will very quickly give you a good indication of what the  most popular pieces of research  are in your field.

One downside of Google Scholar is that it’s merely a search engine – that is, it lists the articles, but oftentimes  it doesn’t host the articles . So you’ll often hit a paywall when clicking through to journal websites. 

Thankfully, your university should provide you with access to their library, so you can find the article titles using Google Scholar and then search for them by name in your university’s online library. Your university may also provide you with access to  ResearchGate , which is another great source for existing research. 

Remember, the correct search keywords will be super important to get the right information from the start. So, pay close attention to the keywords used in the journal articles you read and use those keywords to search for more articles. If you can’t find a spoon in the kitchen, you haven’t looked in the right drawer. 

Need a helping hand?

How should I structure my literature review?

Unfortunately, there’s no generic universal answer for this one. The structure of your literature review will depend largely on your topic area and your research aims and objectives.

You could potentially structure your literature review chapter according to theme, group, variables , chronologically or per concepts in your field of research. We explain the main approaches to structuring your literature review here . You can also download a copy of our free literature review template to help you establish an initial structure.

In general, it’s also a good idea to start wide (i.e. the big-picture-level) and then narrow down, ending your literature review close to your research questions . However, there’s no universal one “right way” to structure your literature review. The most important thing is not to discuss your sources one after the other like a list – as we touched on earlier, your literature review needs to synthesise the research , not summarise it .

Ultimately, you need to craft your literature review so that it conveys the most important information effectively – it needs to tell a logical story in a digestible way. It’s no use starting off with highly technical terms and then only explaining what these terms mean later. Always assume your reader is not a subject matter expert and hold their hand through a journe y of the literature while keeping the functions of the literature review chapter (which we discussed earlier) front of mind.

Example of a literature review

In the video below, we walk you through a high-quality literature review from a dissertation that earned full distinction. This will give you a clearer view of what a strong literature review looks like in practice and hopefully provide some inspiration for your own. 

Wrapping Up

In this post, we’ve (hopefully) answered the question, “ what is a literature review? “. We’ve also considered the purpose and functions of the literature review, as well as how to find literature and how to structure the literature review chapter. If you’re keen to learn more, check out the literature review section of the Grad Coach blog , as well as our detailed video post covering how to write a literature review . 

Psst… there’s more!

This post is an extract from our bestselling short course, Literature Review Bootcamp . If you want to work smart, you don't want to miss this .

16 Comments

Thanks for this review. It narrates what’s not been taught as tutors are always in a early to finish their classes.

Thanks for the kind words, Becky. Good luck with your literature review 🙂

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Timothy T. Chol [email protected]

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Great Brief Explanation, thanks

So helpful to me as a student

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This is an amazing talk. I paved way for myself as a researcher. Thank you GradCoach!

Well-presented overview of the literature!

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Types of Literature Review

There are many types of literature review. The choice of a specific type depends on your research approach and design. The following types of literature review are the most popular in business studies:

Narrative literature review , also referred to as traditional literature review, critiques literature and summarizes the body of a literature. Narrative review also draws conclusions about the topic and identifies gaps or inconsistencies in a body of knowledge. You need to have a sufficiently focused research question to conduct a narrative literature review

Systematic literature review requires more rigorous and well-defined approach compared to most other types of literature review. Systematic literature review is comprehensive and details the timeframe within which the literature was selected. Systematic literature review can be divided into two categories: meta-analysis and meta-synthesis.

When you conduct meta-analysis you take findings from several studies on the same subject and analyze these using standardized statistical procedures. In meta-analysis patterns and relationships are detected and conclusions are drawn. Meta-analysis is associated with deductive research approach.

Meta-synthesis, on the other hand, is based on non-statistical techniques. This technique integrates, evaluates and interprets findings of multiple qualitative research studies. Meta-synthesis literature review is conducted usually when following inductive research approach.

Scoping literature review , as implied by its name is used to identify the scope or coverage of a body of literature on a given topic. It has been noted that “scoping reviews are useful for examining emerging evidence when it is still unclear what other, more specific questions can be posed and valuably addressed by a more precise systematic review.” [1] The main difference between systematic and scoping types of literature review is that, systematic literature review is conducted to find answer to more specific research questions, whereas scoping literature review is conducted to explore more general research question.

Argumentative literature review , as the name implies, examines literature selectively in order to support or refute an argument, deeply imbedded assumption, or philosophical problem already established in the literature. It should be noted that a potential for bias is a major shortcoming associated with argumentative literature review.

Integrative literature review reviews , critiques, and synthesizes secondary data about research topic in an integrated way such that new frameworks and perspectives on the topic are generated. If your research does not involve primary data collection and data analysis, then using integrative literature review will be your only option.

Theoretical literature review focuses on a pool of theory that has accumulated in regard to an issue, concept, theory, phenomena. Theoretical literature reviews play an instrumental role in establishing what theories already exist, the relationships between them, to what degree existing theories have been investigated, and to develop new hypotheses to be tested.

At the earlier parts of the literature review chapter, you need to specify the type of your literature review your chose and justify your choice. Your choice of a specific type of literature review should be based upon your research area, research problem and research methods.  Also, you can briefly discuss other most popular types of literature review mentioned above, to illustrate your awareness of them.

[1] Munn, A. et. al. (2018) “Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach” BMC Medical Research Methodology

  John Dudovskiy

Literature Review: Lit Review Types

• Lit Review Types
• GRADE System
• Do a Lit Review
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• Lit Review Sources
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Types of literature Reviews

[For a compiled list of review types, see: "Meeting the review family: exploring review types and associated information retrieval requirements" :  https://doi.org/10.1111/hir.12276 ]

Traditional or Narrative literature Review

• Critiques and summarizes a body of literature
• Draws conclusions about the topic
• Identifies gaps or inconsistencies in a body of knowledge
• Requires a sufficiently focused research question

Weaknesses:

• A large number of studies may make it difficult to draw conclusions
• The process is subject to bias that supports the researcher's own work.

Systematic Literature Review

• More rigorous and well-defined approach
• Comprehensive
• Published and unpublished studies relating to a particular subject area
• Details the time frame within which the literature was selected
• Details the methods used to evaluate and synthesize findings of the studies in question

Example of systematic review

Meta-analysis

• A form of systematic review (reductive)
• Takes findings from several studies on the same subject and analyzes them using standardized statistical procedures
• Integrates findings from a large body of quantitative findings to enhance under-standing (study=unit of analysis)
• Draws conclusions and detect patterns and relationships

Example of meta-analysis

Meta-synthesis

• Non-statistical technique
• Integrates, evaluates and interprets findings of multiple qualitative research studies
• Identifies common core elements and themes
• May use findings from phenomenological, grounded theory or ethnographic studies
• Involves analyzing and synthesizing key elements
• Goal:  transform individual findings into new conceptualizations and interpretations

Example of meta-synthesis

Systematic Review Resources

• Systematic Reviews: the process: Types of Reviews A full list of types of reviews with definitions from Duke University Medical Center Library and Archives.
• SR Database Cheat Sheet Created 2020 by Taubman Health Sciences Library

See Also: Systematic Review LibGuide

• AMSTAR - Assessing the Methodological Quality of Systematic Reviews
• AMSTAR 2: Appraisal tool for systematic reviews of randomized and observational studies (non-randomized studies)
• Campbell Systematic Reviews A peer-reviewed online monograph series of systematic reviews with a focus on international research evidence on the effects of interventions in crime and justice, education, international development, disability and social welfare.
• CASP Appraisal Checklists "This set of eight critical appraisal tools are designed to be used when reading research, these include tools for Systematic Reviews, Randomised Controlled Trials, Cohort Studies, Case Control Studies, Economic Evaluations, Diagnostic Studies, Qualitative studies and Clinical Prediction Rule." (Free download under Creative Commons License)
• Cochrane Library This link opens in a new window Collection of six databases in medicine and healthcare that contain different types of independent evidence to inform clinical decision-making.
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Literature review.

• What is a Literature Review?
• What is Its Purpose?
• 1. Select a Topic
• 2. Set the Topic in Context
• 3. Types of Information Sources
• 4. Use Information Sources
• 5. Get the Information
• 6. Organize / Manage the Information
• 7. Position the Literature Review
• 8. Write the Literature Review

A literature review is a comprehensive summary of previous research on a topic. The literature review surveys scholarly articles, books, and other sources relevant to a particular area of research.  The review should enumerate, describe, summarize, objectively evaluate and clarify this previous research.  It should give a theoretical base for the research and help you (the author) determine the nature of your research.  The literature review acknowledges the work of previous researchers, and in so doing, assures the reader that your work has been well conceived.  It is assumed that by mentioning a previous work in the field of study, that the author has read, evaluated, and assimiliated that work into the work at hand.

A literature review creates a "landscape" for the reader, giving her or him a full understanding of the developments in the field.  This landscape informs the reader that the author has indeed assimilated all (or the vast majority of) previous, significant works in the field into her or his research. 

 "In writing the literature review, the purpose is to convey to the reader what knowledge and ideas have been established on a topic, and what their strengths and weaknesses are. The literature review must be defined by a guiding concept (eg. your research objective, the problem or issue you are discussing, or your argumentative thesis). It is not just a descriptive list of the material available, or a set of summaries.( http://www.writing.utoronto.ca/advice/specific-types-of-writing/literature-review )

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• Next: What is Its Purpose? >>
• Last Updated: Oct 2, 2023 12:34 PM

What is a Literature Review? How to Write It (with Examples)

A literature review is a critical analysis and synthesis of existing research on a particular topic. It provides an overview of the current state of knowledge, identifies gaps, and highlights key findings in the literature. 1 The purpose of a literature review is to situate your own research within the context of existing scholarship, demonstrating your understanding of the topic and showing how your work contributes to the ongoing conversation in the field. Learning how to write a literature review is a critical tool for successful research. Your ability to summarize and synthesize prior research pertaining to a certain topic demonstrates your grasp on the topic of study, and assists in the learning process. 

Table of Contents

• What is the purpose of literature review? 
• a. Habitat Loss and Species Extinction: 
• b. Range Shifts and Phenological Changes: 
• c. Ocean Acidification and Coral Reefs: 
• d. Adaptive Strategies and Conservation Efforts: 

How to write a good literature review 

• Choose a Topic and Define the Research Question: 
• Decide on the Scope of Your Review: 
• Select Databases for Searches: 
• Conduct Searches and Keep Track: 
• Review the Literature: 
• Organize and Write Your Literature Review: 
• How to write a literature review faster with Paperpal? 
• Frequently asked questions 

What is a literature review?

A well-conducted literature review demonstrates the researcher’s familiarity with the existing literature, establishes the context for their own research, and contributes to scholarly conversations on the topic. One of the purposes of a literature review is also to help researchers avoid duplicating previous work and ensure that their research is informed by and builds upon the existing body of knowledge.

What is the purpose of literature review?

A literature review serves several important purposes within academic and research contexts. Here are some key objectives and functions of a literature review: 2  

1. Contextualizing the Research Problem: The literature review provides a background and context for the research problem under investigation. It helps to situate the study within the existing body of knowledge. 

2. Identifying Gaps in Knowledge: By identifying gaps, contradictions, or areas requiring further research, the researcher can shape the research question and justify the significance of the study. This is crucial for ensuring that the new research contributes something novel to the field. 

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3. Understanding Theoretical and Conceptual Frameworks: Literature reviews help researchers gain an understanding of the theoretical and conceptual frameworks used in previous studies. This aids in the development of a theoretical framework for the current research. 

4. Providing Methodological Insights: Another purpose of literature reviews is that it allows researchers to learn about the methodologies employed in previous studies. This can help in choosing appropriate research methods for the current study and avoiding pitfalls that others may have encountered. 

5. Establishing Credibility: A well-conducted literature review demonstrates the researcher’s familiarity with existing scholarship, establishing their credibility and expertise in the field. It also helps in building a solid foundation for the new research. 

6. Informing Hypotheses or Research Questions: The literature review guides the formulation of hypotheses or research questions by highlighting relevant findings and areas of uncertainty in existing literature. 

Literature review example

Let’s delve deeper with a literature review example: Let’s say your literature review is about the impact of climate change on biodiversity. You might format your literature review into sections such as the effects of climate change on habitat loss and species extinction, phenological changes, and marine biodiversity. Each section would then summarize and analyze relevant studies in those areas, highlighting key findings and identifying gaps in the research. The review would conclude by emphasizing the need for further research on specific aspects of the relationship between climate change and biodiversity. The following literature review template provides a glimpse into the recommended literature review structure and content, demonstrating how research findings are organized around specific themes within a broader topic. 

Literature Review on Climate Change Impacts on Biodiversity:

Climate change is a global phenomenon with far-reaching consequences, including significant impacts on biodiversity. This literature review synthesizes key findings from various studies: 

a. Habitat Loss and Species Extinction:

Climate change-induced alterations in temperature and precipitation patterns contribute to habitat loss, affecting numerous species (Thomas et al., 2004). The review discusses how these changes increase the risk of extinction, particularly for species with specific habitat requirements. 

b. Range Shifts and Phenological Changes:

Observations of range shifts and changes in the timing of biological events (phenology) are documented in response to changing climatic conditions (Parmesan & Yohe, 2003). These shifts affect ecosystems and may lead to mismatches between species and their resources. 

c. Ocean Acidification and Coral Reefs:

The review explores the impact of climate change on marine biodiversity, emphasizing ocean acidification’s threat to coral reefs (Hoegh-Guldberg et al., 2007). Changes in pH levels negatively affect coral calcification, disrupting the delicate balance of marine ecosystems. 

d. Adaptive Strategies and Conservation Efforts:

Recognizing the urgency of the situation, the literature review discusses various adaptive strategies adopted by species and conservation efforts aimed at mitigating the impacts of climate change on biodiversity (Hannah et al., 2007). It emphasizes the importance of interdisciplinary approaches for effective conservation planning. 

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Writing a literature review involves summarizing and synthesizing existing research on a particular topic. A good literature review format should include the following elements. 

Introduction: The introduction sets the stage for your literature review, providing context and introducing the main focus of your review. 

• Opening Statement: Begin with a general statement about the broader topic and its significance in the field. 
• Scope and Purpose: Clearly define the scope of your literature review. Explain the specific research question or objective you aim to address. 
• Organizational Framework: Briefly outline the structure of your literature review, indicating how you will categorize and discuss the existing research. 
• Significance of the Study: Highlight why your literature review is important and how it contributes to the understanding of the chosen topic. 
• Thesis Statement: Conclude the introduction with a concise thesis statement that outlines the main argument or perspective you will develop in the body of the literature review. 

Body: The body of the literature review is where you provide a comprehensive analysis of existing literature, grouping studies based on themes, methodologies, or other relevant criteria. 

• Organize by Theme or Concept: Group studies that share common themes, concepts, or methodologies. Discuss each theme or concept in detail, summarizing key findings and identifying gaps or areas of disagreement. 
• Critical Analysis: Evaluate the strengths and weaknesses of each study. Discuss the methodologies used, the quality of evidence, and the overall contribution of each work to the understanding of the topic. 
• Synthesis of Findings: Synthesize the information from different studies to highlight trends, patterns, or areas of consensus in the literature. 
• Identification of Gaps: Discuss any gaps or limitations in the existing research and explain how your review contributes to filling these gaps. 
• Transition between Sections: Provide smooth transitions between different themes or concepts to maintain the flow of your literature review. 

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Conclusion: The conclusion of your literature review should summarize the main findings, highlight the contributions of the review, and suggest avenues for future research. 

• Summary of Key Findings: Recap the main findings from the literature and restate how they contribute to your research question or objective. 
• Contributions to the Field: Discuss the overall contribution of your literature review to the existing knowledge in the field. 
• Implications and Applications: Explore the practical implications of the findings and suggest how they might impact future research or practice. 
• Recommendations for Future Research: Identify areas that require further investigation and propose potential directions for future research in the field. 
• Final Thoughts: Conclude with a final reflection on the importance of your literature review and its relevance to the broader academic community. 

Conducting a literature review

Conducting a literature review is an essential step in research that involves reviewing and analyzing existing literature on a specific topic. It’s important to know how to do a literature review effectively, so here are the steps to follow: 1  

Choose a Topic and Define the Research Question:

• Select a topic that is relevant to your field of study. 
• Clearly define your research question or objective. Determine what specific aspect of the topic do you want to explore? 

Decide on the Scope of Your Review:

• Determine the timeframe for your literature review. Are you focusing on recent developments, or do you want a historical overview? 
• Consider the geographical scope. Is your review global, or are you focusing on a specific region? 
• Define the inclusion and exclusion criteria. What types of sources will you include? Are there specific types of studies or publications you will exclude? 

Select Databases for Searches:

• Identify relevant databases for your field. Examples include PubMed, IEEE Xplore, Scopus, Web of Science, and Google Scholar. 
• Consider searching in library catalogs, institutional repositories, and specialized databases related to your topic. 

Conduct Searches and Keep Track:

• Develop a systematic search strategy using keywords, Boolean operators (AND, OR, NOT), and other search techniques. 
• Record and document your search strategy for transparency and replicability. 
• Keep track of the articles, including publication details, abstracts, and links. Use citation management tools like EndNote, Zotero, or Mendeley to organize your references. 

Review the Literature:

• Evaluate the relevance and quality of each source. Consider the methodology, sample size, and results of studies. 
• Organize the literature by themes or key concepts. Identify patterns, trends, and gaps in the existing research. 
• Summarize key findings and arguments from each source. Compare and contrast different perspectives. 
• Identify areas where there is a consensus in the literature and where there are conflicting opinions. 
• Provide critical analysis and synthesis of the literature. What are the strengths and weaknesses of existing research? 

Organize and Write Your Literature Review:

• Literature review outline should be based on themes, chronological order, or methodological approaches. 
• Write a clear and coherent narrative that synthesizes the information gathered. 
• Use proper citations for each source and ensure consistency in your citation style (APA, MLA, Chicago, etc.). 
• Conclude your literature review by summarizing key findings, identifying gaps, and suggesting areas for future research. 

Whether you’re exploring a new research field or finding new angles to develop an existing topic, sifting through hundreds of papers can take more time than you have to spare. But what if you could find science-backed insights with verified citations in seconds? That’s the power of Paperpal’s new Research feature!  

How to write a literature review faster with Paperpal?

Paperpal, an AI writing assistant, integrates powerful academic search capabilities within its writing platform. With the Research feature, you get 100% factual insights, with citations backed by 250M+ verified research articles, directly within your writing interface with the option to save relevant references in your Citation Library. By eliminating the need to switch tabs to find answers to all your research questions, Paperpal saves time and helps you stay focused on your writing.   

Here’s how to use the Research feature:  

• Ask a question: Get started with a new document on paperpal.com. Click on the “Research” feature and type your question in plain English. Paperpal will scour over 250 million research articles, including conference papers and preprints, to provide you with accurate insights and citations. 
• Review and Save: Paperpal summarizes the information, while citing sources and listing relevant reads. You can quickly scan the results to identify relevant references and save these directly to your built-in citations library for later access. 
• Cite with Confidence: Paperpal makes it easy to incorporate relevant citations and references into your writing, ensuring your arguments are well-supported by credible sources. This translates to a polished, well-researched literature review. 

The literature review sample and detailed advice on writing and conducting a review will help you produce a well-structured report. But remember that a good literature review is an ongoing process, and it may be necessary to revisit and update it as your research progresses. By combining effortless research with an easy citation process, Paperpal Research streamlines the literature review process and empowers you to write faster and with more confidence. Try Paperpal Research now and see for yourself.  

Frequently asked questions

A literature review is a critical and comprehensive analysis of existing literature (published and unpublished works) on a specific topic or research question and provides a synthesis of the current state of knowledge in a particular field. A well-conducted literature review is crucial for researchers to build upon existing knowledge, avoid duplication of efforts, and contribute to the advancement of their field. It also helps researchers situate their work within a broader context and facilitates the development of a sound theoretical and conceptual framework for their studies.

Literature review is a crucial component of research writing, providing a solid background for a research paper’s investigation. The aim is to keep professionals up to date by providing an understanding of ongoing developments within a specific field, including research methods, and experimental techniques used in that field, and present that knowledge in the form of a written report. Also, the depth and breadth of the literature review emphasizes the credibility of the scholar in his or her field.  

Before writing a literature review, it’s essential to undertake several preparatory steps to ensure that your review is well-researched, organized, and focused. This includes choosing a topic of general interest to you and doing exploratory research on that topic, writing an annotated bibliography, and noting major points, especially those that relate to the position you have taken on the topic. 

Literature reviews and academic research papers are essential components of scholarly work but serve different purposes within the academic realm. 3 A literature review aims to provide a foundation for understanding the current state of research on a particular topic, identify gaps or controversies, and lay the groundwork for future research. Therefore, it draws heavily from existing academic sources, including books, journal articles, and other scholarly publications. In contrast, an academic research paper aims to present new knowledge, contribute to the academic discourse, and advance the understanding of a specific research question. Therefore, it involves a mix of existing literature (in the introduction and literature review sections) and original data or findings obtained through research methods. 

Literature reviews are essential components of academic and research papers, and various strategies can be employed to conduct them effectively. If you want to know how to write a literature review for a research paper, here are four common approaches that are often used by researchers.  Chronological Review: This strategy involves organizing the literature based on the chronological order of publication. It helps to trace the development of a topic over time, showing how ideas, theories, and research have evolved.  Thematic Review: Thematic reviews focus on identifying and analyzing themes or topics that cut across different studies. Instead of organizing the literature chronologically, it is grouped by key themes or concepts, allowing for a comprehensive exploration of various aspects of the topic.  Methodological Review: This strategy involves organizing the literature based on the research methods employed in different studies. It helps to highlight the strengths and weaknesses of various methodologies and allows the reader to evaluate the reliability and validity of the research findings.  Theoretical Review: A theoretical review examines the literature based on the theoretical frameworks used in different studies. This approach helps to identify the key theories that have been applied to the topic and assess their contributions to the understanding of the subject.  It’s important to note that these strategies are not mutually exclusive, and a literature review may combine elements of more than one approach. The choice of strategy depends on the research question, the nature of the literature available, and the goals of the review. Additionally, other strategies, such as integrative reviews or systematic reviews, may be employed depending on the specific requirements of the research.

The literature review format can vary depending on the specific publication guidelines. However, there are some common elements and structures that are often followed. Here is a general guideline for the format of a literature review:  Introduction:   Provide an overview of the topic.  Define the scope and purpose of the literature review.  State the research question or objective.  Body:   Organize the literature by themes, concepts, or chronology.  Critically analyze and evaluate each source.  Discuss the strengths and weaknesses of the studies.  Highlight any methodological limitations or biases.  Identify patterns, connections, or contradictions in the existing research.  Conclusion:   Summarize the key points discussed in the literature review.  Highlight the research gap.  Address the research question or objective stated in the introduction.  Highlight the contributions of the review and suggest directions for future research.

Both annotated bibliographies and literature reviews involve the examination of scholarly sources. While annotated bibliographies focus on individual sources with brief annotations, literature reviews provide a more in-depth, integrated, and comprehensive analysis of existing literature on a specific topic. The key differences are as follows: 

References 

• Denney, A. S., & Tewksbury, R. (2013). How to write a literature review.  Journal of criminal justice education ,  24 (2), 218-234. 
• Pan, M. L. (2016).  Preparing literature reviews: Qualitative and quantitative approaches . Taylor & Francis. 
• Cantero, C. (2019). How to write a literature review.  San José State University Writing Center . 

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Ten Simple Rules for Writing a Literature Review

Marco pautasso.

1 Centre for Functional and Evolutionary Ecology (CEFE), CNRS, Montpellier, France

2 Centre for Biodiversity Synthesis and Analysis (CESAB), FRB, Aix-en-Provence, France

Literature reviews are in great demand in most scientific fields. Their need stems from the ever-increasing output of scientific publications [1] . For example, compared to 1991, in 2008 three, eight, and forty times more papers were indexed in Web of Science on malaria, obesity, and biodiversity, respectively [2] . Given such mountains of papers, scientists cannot be expected to examine in detail every single new paper relevant to their interests [3] . Thus, it is both advantageous and necessary to rely on regular summaries of the recent literature. Although recognition for scientists mainly comes from primary research, timely literature reviews can lead to new synthetic insights and are often widely read [4] . For such summaries to be useful, however, they need to be compiled in a professional way [5] .

When starting from scratch, reviewing the literature can require a titanic amount of work. That is why researchers who have spent their career working on a certain research issue are in a perfect position to review that literature. Some graduate schools are now offering courses in reviewing the literature, given that most research students start their project by producing an overview of what has already been done on their research issue [6] . However, it is likely that most scientists have not thought in detail about how to approach and carry out a literature review.

Reviewing the literature requires the ability to juggle multiple tasks, from finding and evaluating relevant material to synthesising information from various sources, from critical thinking to paraphrasing, evaluating, and citation skills [7] . In this contribution, I share ten simple rules I learned working on about 25 literature reviews as a PhD and postdoctoral student. Ideas and insights also come from discussions with coauthors and colleagues, as well as feedback from reviewers and editors.

Rule 1: Define a Topic and Audience

How to choose which topic to review? There are so many issues in contemporary science that you could spend a lifetime of attending conferences and reading the literature just pondering what to review. On the one hand, if you take several years to choose, several other people may have had the same idea in the meantime. On the other hand, only a well-considered topic is likely to lead to a brilliant literature review [8] . The topic must at least be:

• interesting to you (ideally, you should have come across a series of recent papers related to your line of work that call for a critical summary),
• an important aspect of the field (so that many readers will be interested in the review and there will be enough material to write it), and
• a well-defined issue (otherwise you could potentially include thousands of publications, which would make the review unhelpful).

Ideas for potential reviews may come from papers providing lists of key research questions to be answered [9] , but also from serendipitous moments during desultory reading and discussions. In addition to choosing your topic, you should also select a target audience. In many cases, the topic (e.g., web services in computational biology) will automatically define an audience (e.g., computational biologists), but that same topic may also be of interest to neighbouring fields (e.g., computer science, biology, etc.).

Rule 2: Search and Re-search the Literature

After having chosen your topic and audience, start by checking the literature and downloading relevant papers. Five pieces of advice here:

• keep track of the search items you use (so that your search can be replicated [10] ),
• keep a list of papers whose pdfs you cannot access immediately (so as to retrieve them later with alternative strategies),
• use a paper management system (e.g., Mendeley, Papers, Qiqqa, Sente),
• define early in the process some criteria for exclusion of irrelevant papers (these criteria can then be described in the review to help define its scope), and
• do not just look for research papers in the area you wish to review, but also seek previous reviews.

The chances are high that someone will already have published a literature review ( Figure 1 ), if not exactly on the issue you are planning to tackle, at least on a related topic. If there are already a few or several reviews of the literature on your issue, my advice is not to give up, but to carry on with your own literature review,

The bottom-right situation (many literature reviews but few research papers) is not just a theoretical situation; it applies, for example, to the study of the impacts of climate change on plant diseases, where there appear to be more literature reviews than research studies [33] .

• discussing in your review the approaches, limitations, and conclusions of past reviews,
• trying to find a new angle that has not been covered adequately in the previous reviews, and
• incorporating new material that has inevitably accumulated since their appearance.

When searching the literature for pertinent papers and reviews, the usual rules apply:

• be thorough,
• use different keywords and database sources (e.g., DBLP, Google Scholar, ISI Proceedings, JSTOR Search, Medline, Scopus, Web of Science), and
• look at who has cited past relevant papers and book chapters.

Rule 3: Take Notes While Reading

If you read the papers first, and only afterwards start writing the review, you will need a very good memory to remember who wrote what, and what your impressions and associations were while reading each single paper. My advice is, while reading, to start writing down interesting pieces of information, insights about how to organize the review, and thoughts on what to write. This way, by the time you have read the literature you selected, you will already have a rough draft of the review.

Of course, this draft will still need much rewriting, restructuring, and rethinking to obtain a text with a coherent argument [11] , but you will have avoided the danger posed by staring at a blank document. Be careful when taking notes to use quotation marks if you are provisionally copying verbatim from the literature. It is advisable then to reformulate such quotes with your own words in the final draft. It is important to be careful in noting the references already at this stage, so as to avoid misattributions. Using referencing software from the very beginning of your endeavour will save you time.

Rule 4: Choose the Type of Review You Wish to Write

After having taken notes while reading the literature, you will have a rough idea of the amount of material available for the review. This is probably a good time to decide whether to go for a mini- or a full review. Some journals are now favouring the publication of rather short reviews focusing on the last few years, with a limit on the number of words and citations. A mini-review is not necessarily a minor review: it may well attract more attention from busy readers, although it will inevitably simplify some issues and leave out some relevant material due to space limitations. A full review will have the advantage of more freedom to cover in detail the complexities of a particular scientific development, but may then be left in the pile of the very important papers “to be read” by readers with little time to spare for major monographs.

There is probably a continuum between mini- and full reviews. The same point applies to the dichotomy of descriptive vs. integrative reviews. While descriptive reviews focus on the methodology, findings, and interpretation of each reviewed study, integrative reviews attempt to find common ideas and concepts from the reviewed material [12] . A similar distinction exists between narrative and systematic reviews: while narrative reviews are qualitative, systematic reviews attempt to test a hypothesis based on the published evidence, which is gathered using a predefined protocol to reduce bias [13] , [14] . When systematic reviews analyse quantitative results in a quantitative way, they become meta-analyses. The choice between different review types will have to be made on a case-by-case basis, depending not just on the nature of the material found and the preferences of the target journal(s), but also on the time available to write the review and the number of coauthors [15] .

Rule 5: Keep the Review Focused, but Make It of Broad Interest

Whether your plan is to write a mini- or a full review, it is good advice to keep it focused 16 , 17 . Including material just for the sake of it can easily lead to reviews that are trying to do too many things at once. The need to keep a review focused can be problematic for interdisciplinary reviews, where the aim is to bridge the gap between fields [18] . If you are writing a review on, for example, how epidemiological approaches are used in modelling the spread of ideas, you may be inclined to include material from both parent fields, epidemiology and the study of cultural diffusion. This may be necessary to some extent, but in this case a focused review would only deal in detail with those studies at the interface between epidemiology and the spread of ideas.

While focus is an important feature of a successful review, this requirement has to be balanced with the need to make the review relevant to a broad audience. This square may be circled by discussing the wider implications of the reviewed topic for other disciplines.

Rule 6: Be Critical and Consistent

Reviewing the literature is not stamp collecting. A good review does not just summarize the literature, but discusses it critically, identifies methodological problems, and points out research gaps [19] . After having read a review of the literature, a reader should have a rough idea of:

• the major achievements in the reviewed field,
• the main areas of debate, and
• the outstanding research questions.

It is challenging to achieve a successful review on all these fronts. A solution can be to involve a set of complementary coauthors: some people are excellent at mapping what has been achieved, some others are very good at identifying dark clouds on the horizon, and some have instead a knack at predicting where solutions are going to come from. If your journal club has exactly this sort of team, then you should definitely write a review of the literature! In addition to critical thinking, a literature review needs consistency, for example in the choice of passive vs. active voice and present vs. past tense.

Rule 7: Find a Logical Structure

Like a well-baked cake, a good review has a number of telling features: it is worth the reader's time, timely, systematic, well written, focused, and critical. It also needs a good structure. With reviews, the usual subdivision of research papers into introduction, methods, results, and discussion does not work or is rarely used. However, a general introduction of the context and, toward the end, a recapitulation of the main points covered and take-home messages make sense also in the case of reviews. For systematic reviews, there is a trend towards including information about how the literature was searched (database, keywords, time limits) [20] .

How can you organize the flow of the main body of the review so that the reader will be drawn into and guided through it? It is generally helpful to draw a conceptual scheme of the review, e.g., with mind-mapping techniques. Such diagrams can help recognize a logical way to order and link the various sections of a review [21] . This is the case not just at the writing stage, but also for readers if the diagram is included in the review as a figure. A careful selection of diagrams and figures relevant to the reviewed topic can be very helpful to structure the text too [22] .

Rule 8: Make Use of Feedback

Reviews of the literature are normally peer-reviewed in the same way as research papers, and rightly so [23] . As a rule, incorporating feedback from reviewers greatly helps improve a review draft. Having read the review with a fresh mind, reviewers may spot inaccuracies, inconsistencies, and ambiguities that had not been noticed by the writers due to rereading the typescript too many times. It is however advisable to reread the draft one more time before submission, as a last-minute correction of typos, leaps, and muddled sentences may enable the reviewers to focus on providing advice on the content rather than the form.

Feedback is vital to writing a good review, and should be sought from a variety of colleagues, so as to obtain a diversity of views on the draft. This may lead in some cases to conflicting views on the merits of the paper, and on how to improve it, but such a situation is better than the absence of feedback. A diversity of feedback perspectives on a literature review can help identify where the consensus view stands in the landscape of the current scientific understanding of an issue [24] .

Rule 9: Include Your Own Relevant Research, but Be Objective

In many cases, reviewers of the literature will have published studies relevant to the review they are writing. This could create a conflict of interest: how can reviewers report objectively on their own work [25] ? Some scientists may be overly enthusiastic about what they have published, and thus risk giving too much importance to their own findings in the review. However, bias could also occur in the other direction: some scientists may be unduly dismissive of their own achievements, so that they will tend to downplay their contribution (if any) to a field when reviewing it.

In general, a review of the literature should neither be a public relations brochure nor an exercise in competitive self-denial. If a reviewer is up to the job of producing a well-organized and methodical review, which flows well and provides a service to the readership, then it should be possible to be objective in reviewing one's own relevant findings. In reviews written by multiple authors, this may be achieved by assigning the review of the results of a coauthor to different coauthors.

Rule 10: Be Up-to-Date, but Do Not Forget Older Studies

Given the progressive acceleration in the publication of scientific papers, today's reviews of the literature need awareness not just of the overall direction and achievements of a field of inquiry, but also of the latest studies, so as not to become out-of-date before they have been published. Ideally, a literature review should not identify as a major research gap an issue that has just been addressed in a series of papers in press (the same applies, of course, to older, overlooked studies (“sleeping beauties” [26] )). This implies that literature reviewers would do well to keep an eye on electronic lists of papers in press, given that it can take months before these appear in scientific databases. Some reviews declare that they have scanned the literature up to a certain point in time, but given that peer review can be a rather lengthy process, a full search for newly appeared literature at the revision stage may be worthwhile. Assessing the contribution of papers that have just appeared is particularly challenging, because there is little perspective with which to gauge their significance and impact on further research and society.

Inevitably, new papers on the reviewed topic (including independently written literature reviews) will appear from all quarters after the review has been published, so that there may soon be the need for an updated review. But this is the nature of science [27] – [32] . I wish everybody good luck with writing a review of the literature.

Acknowledgments

Many thanks to M. Barbosa, K. Dehnen-Schmutz, T. Döring, D. Fontaneto, M. Garbelotto, O. Holdenrieder, M. Jeger, D. Lonsdale, A. MacLeod, P. Mills, M. Moslonka-Lefebvre, G. Stancanelli, P. Weisberg, and X. Xu for insights and discussions, and to P. Bourne, T. Matoni, and D. Smith for helpful comments on a previous draft.

Funding Statement

This work was funded by the French Foundation for Research on Biodiversity (FRB) through its Centre for Synthesis and Analysis of Biodiversity data (CESAB), as part of the NETSEED research project. The funders had no role in the preparation of the manuscript.

ON YOUR 1ST ORDER

Different Types of Literature Review: Which One Fits Your Research?

By Laura Brown on 13th October 2023

You might not have heard that there are multiple kinds of literature review. However, with the progress in your academic career you will learn these classifications and may need to use different types of them. However, there is nothing to worry if you aren’t aware of them now, as here we are going to discuss this topic in detail.

There are approximately 14 types of literature review on the basis of their specific objectives, methodologies, and the way they approach and analyse existing literature in academic research. Of those 14, there are 4 major types. But before we delve into the details of each one of them and how they are useful in academics, let’s first understand the basics of literature review.

What is Literature Review?

A literature review is a critical and systematic summary and evaluation of existing research. It is an essential component of academic and research work, providing an overview of the current state of knowledge in a particular field.

In easy words, a literature review is like making a big, organised summary of all the important research and smart books or articles about a particular topic or question. It’s something scholars and researchers do, and it helps everyone see what we already know about that topic. It’s kind of like taking a snapshot of what we understand right now in a certain field.

It serves with some specific purpose in the research.

• Provides a comprehensive understanding of existing research on a topic.
• Identifies gaps, trends, and inconsistencies in the literature.
• Contextualise your own research within the broader academic discourse.
• Supports the development of theoretical frameworks or research hypotheses.

4 Major Types Of Literature Review

The four major types include, Narrative Review, Systematic Review, Meta-Analysis, and Scoping Review. These are known as the major ones because they’re like the “go-to” methods for researchers in academic and research circles. Think of them as the classic tools in the researcher’s toolbox. They’ve earned their reputation because they have a unique style for literature review introduction , clear steps and specific qualities that make them super handy for different research needs.

1. Narrative Review

Narrative reviews present a well-structured narrative that reads like a cohesive story, providing a comprehensive overview of a specific topic. These reviews often incorporate historical context and offer a broad understanding of the subject matter, making them valuable for researchers looking to establish a foundational understanding of their area of interest. They are particularly useful when a historical perspective or a broad context is necessary to comprehend the current state of knowledge in a field.

2. Systematic Review

Systematic reviews are renowned for their methodological rigour. They involve a meticulously structured process that includes the systematic selection of relevant studies, comprehensive data extraction, and a critical synthesis of their findings. This systematic approach is designed to minimise bias and subjectivity, making systematic reviews highly reliable and objective. They are considered the gold standard for evidence-based research as they provide a clear and rigorous assessment of the available evidence on a specific research question.

3. Meta Analysis

Meta analysis is a powerful method for researchers who prefer a quantitative and statistical perspective. It involves the statistical synthesis of data from various studies, allowing researchers to draw more precise and generalisable conclusions by combining data from multiple sources. Meta analyses are especially valuable when the aim is to quantitatively measure the effect size or impact of a particular intervention, treatment, or phenomenon.

4. Scoping Review

Scoping reviews are invaluable tools, especially for researchers in the early stages of exploring a topic. These reviews aim to map the existing literature, identifying gaps and helping clarify research questions. Scoping reviews provide a panoramic view of the available research, which is particularly useful when researchers are embarking on exploratory studies or trying to understand the breadth and depth of a subject before conducting more focused research.

Different Types Of Literature review In Research

There are some more approaches to conduct literature review. Let’s explore these classifications quickly.

5. Critical Review

Critical reviews provide an in-depth evaluation of existing literature, scrutinising sources for their strengths, weaknesses, and relevance. They offer a critical perspective, often highlighting gaps in the research and areas for further investigation.

6. Theoretical Review

Theoretical reviews are centred around exploring and analysing the theoretical frameworks, concepts, and models present in the literature. They aim to contribute to the development and refinement of theoretical perspectives within a specific field.

7. Integrative Review

Integrative reviews synthesise a diverse range of studies, drawing connections between various research findings to create a comprehensive understanding of a topic. These reviews often bridge gaps between different perspectives and provide a holistic overview.

8. Historical Review

Historical reviews focus on the evolution of a topic over time, tracing its development through past research, events, and scholarly contributions. They offer valuable context for understanding the current state of research.

9. Methodological Review

Among the different kinds of literature reviews, methodological reviews delve into the research methods and methodologies employed in existing studies. Researchers assess these approaches for their effectiveness, validity, and relevance to the research question at hand.

10. Cross-Disciplinary Review

Cross-disciplinary reviews explore a topic from multiple academic disciplines, emphasising the diversity of perspectives and insights that each discipline brings. They are particularly useful for interdisciplinary research projects and uncovering connections between seemingly unrelated fields.

11. Descriptive Review

Descriptive reviews provide an organised summary of existing literature without extensive analysis. They offer a straightforward overview of key findings, research methods, and themes present in the reviewed studies.

12. Rapid Review

Rapid reviews expedite the literature review process, focusing on summarising relevant studies quickly. They are often used for time-sensitive projects where efficiency is a priority, without sacrificing quality.

13. Conceptual Review

Conceptual reviews concentrate on clarifying and developing theoretical concepts within a specific field. They address ambiguities or inconsistencies in existing theories, aiming to refine and expand conceptual frameworks.

14. Library Research

Library research reviews rely primarily on library and archival resources to gather and synthesise information. They are often employed in historical or archive-based research projects, utilising library collections and historical documents for in-depth analysis.

Each type of literature review serves distinct purposes and comes with its own set of strengths and weaknesses, allowing researchers to choose the one that best suits their research objectives and questions.

Choosing the Ideal Literature Review Approach in Academics

In order to conduct your research in the right manner, it is important that you choose the correct type of review for your literature. Here are 8 amazing tips we have sorted for you in regard to literature review help so that you can select the best-suited type for your research.

• Clarify Your Research Goals: Begin by defining your research objectives and what you aim to achieve with the literature review. Are you looking to summarise existing knowledge, identify gaps, or analyse specific data?
• Understand Different Review Types: Familiarise yourself with different kinds of literature reviews, including systematic reviews, narrative reviews, meta-analyses, scoping reviews, and integrative reviews. Each serves a different purpose.
• Consider Available Resources: Assess the resources at your disposal, including time, access to databases, and the volume of literature on your topic. Some review types may be more resource-intensive than others.
• Alignment with Research Question: Ensure that the chosen review type aligns with your research question or hypothesis. Some types are better suited for answering specific research questions than others.
• Scope and Depth: Determine the scope and depth of your review. For a broad overview, a narrative review might be suitable, while a systematic review is ideal for an in-depth analysis.
• Consult with Advisors: Seek guidance from your academic advisors or mentors. They can provide valuable insights into which review type best fits your research goals and resources.
• Consider Research Field Standards: Different academic fields have established standards and preferences for different forms of literature review. Familiarise yourself with what is common and accepted in your field.
• Pilot Review: Consider conducting a small-scale pilot review of the literature to test the feasibility and suitability of your chosen review type before committing to a larger project.

Bonus Tip: Crafting an Effective Literature Review

Now, since you have learned all the literature review types and have understood which one to prefer, here are some bonus tips for you to structure a literature review of a dissertation .

• Clearly Define Your Research Question: Start with a well-defined and focused research question to guide your literature review.
• Thorough Search Strategy: Develop a comprehensive search strategy to ensure you capture all relevant literature.
• Critical Evaluation: Assess the quality and credibility of the sources you include in your review.
• Synthesise and Organise: Summarise the key findings and organise the literature into themes or categories.
• Maintain a Systematic Approach: If conducting a systematic review, adhere to a predefined methodology and reporting guidelines.
• Engage in Continuous Review: Regularly update your literature review to incorporate new research and maintain relevance.

Some Useful Tools And Resources For You

Effective literature reviews demand a range of tools and resources to streamline the process.

• Reference management software like EndNote, Zotero, and Mendeley helps organise, store, and cite sources, saving time and ensuring accuracy.
• Academic databases such as PubMed, Google Scholar, and Web of Science provide access to a vast array of scholarly articles, with advanced search and citation tracking features.
• Research guides from universities and libraries offer tips and templates for structuring reviews.
• Research networks like ResearchGate and Academia.edu facilitate collaboration and access to publications. Literature review templates and research workshops provide additional support.

Some Common Mistakes To Avoid

Avoid these common mistakes when crafting literature reviews.

• Unclear research objectives result in unfocused reviews, so start with well-defined questions.
• Biased source selection can compromise objectivity, so include diverse perspectives.
• Never miss on referencing; proper citation and referencing are essential for academic integrity.
• Don’t overlook older literature, which provides foundational insights.
• Be mindful of scope creep, where the review drifts from the research question; stay disciplined to maintain focus and relevance.

While Summing Up On Various Types Of Literature Review

As we conclude this classification of fourteen distinct approaches to conduct literature reviews, it’s clear that the world of research offers a multitude of avenues for understanding, analysing, and contributing to existing knowledge.

Whether you’re a seasoned scholar or a student beginning your academic journey, the choice of review type should align with your research objectives and the nature of your topic. The versatility of these approaches empowers you to tailor your review to the demands of your project.

Remember, your research endeavours have the potential to shape the future of knowledge, so choose wisely and dive into the world of literature reviews with confidence and purpose. Happy reviewing!

Laura Brown, a senior content writer who writes actionable blogs at Crowd Writer.

Writing the Literature Review

Barry Mauer and John Venecek

• The Literature Review

What is the Purpose of the Review?

What is the scope of the review, strategies for getting started, types of literature reviews, composition guidelines, how to locate reviews by discipline, key takeaways.

We also provide the following activities:

Types of Literature Reviews [Refresher]

Writing the literature review [refresher], the literature review [1].

Conducting a literary studies research project involves time and effort, with much of it going towards the development of a literature review . A literature review might fill several pages of your research paper and usually appears soon after an introduction but before you present your detailed argument. A literature review provides your audience with an overview of the available research about your area(s) of study, including the literary work, your theory, and methodology. The literature review demonstrates how these scholarly discussions have changed over time, and it allows you to position your research in relation to research that has come before yours. Your aim is to present the discussion up to this point. Depending on the nature of the assignment, you may also include your critical commentary on prior research, noting among this material the weaker and stronger arguments, breakthroughs and dead ends, blind spots and opportunities, the invention of key terms and methods, mistakes as well as misreadings, and so on.

Once you have gathered the research materials you need for your literature review, you have another task: conducting an analysis on the research to see where your original contribution fits into the scholarly conversation. As the saying goes, “we are standing on the shoulders of giants.” Your job is to show a portrait of these giants to your audience, and to show how your work relates to the portrait. On many scholarly topics, literature reviews already exist. You may refer to such existing reviews within your own, indicating any materials might have been overlooked, new developments that have arisen since the publication of the existing literature review, and new perspectives or insights you have about the materials.

Some beginning researchers try to tear down the work of other researchers in an effort to make their own work look good by comparison. It rarely works. First, it tends to make your audience skeptical of your claims. Second, it ignores the fact that even the mistakes, blind spots, and failures of other researchers contribute something to our knowledge. Albert Einstein didn’t disrespect Sir Isaac Newton by saying Newton’s theory of space was wrong and terrible and that Einstein’s own theory was great by comparison. He built upon Newton’s work, showing how it could be improved. If, however, a researcher willfully set out to deceive or distort or to tear down the work of other scholars without good reason, then their work does not deserve such deference.

Most literature reviews appear after the introduction. It presents your reader with relevant information about the scholarly discussion up to now. Later in your paper, you discuss your contribution. Before you begin work on your literature review, let’s discuss what we mean by “literature”; understand the purpose and scope of the review; establish criteria for selecting, organizing, and interpreting your findings; and discuss how to connect your findings to your research question.

Many students seek to “find sources that agree with my claim or idea.” That approach is too narrow, in our view. If we use such an approach, we may get the following results:

• Because we can find sources that agree with almost any claim, readers will wonder whether your claims are weak and the sources are cherry picked.
• While literary scholars sometimes cite authorities to support their claims, they don’t rely only on authority. They respect authority, but not too much. Your own claims need to rely more on evidence (from the literary text, historical and biographical information), and your critical and creative reasoning skills.
• Scholarship is a conversation; thus, the goal is less about finding agreement and more about joining the conversation with the aim of making a valuable contribution to the discussion.

The literature review provides your reader with an overview of the existing research about your topic or problem. It provides the context necessary for your reader to catch up with the scholarly conversation and then to appreciate the value of your contribution to it. The literature review sharpens the focus of your research and demonstrates your knowledge and understanding of the scholarly conversation around your topic, which, in turn, helps establish your credibility as a researcher.

Creating the literature review involves more than gathering citations. It is a qualitative process through which you will discover what is already known about your topic, and identify the key authorities, methods, and theoretical foundations, so you can begin to position your contributions within the scholarly conversation.

Defining the scope of your review will also help you establish criteria to determine the relevance of the sources you are finding. At this stage, you are not reading in-depth; instead, you are skimming through what has already been published and identifying the major concepts, theories, methodologies, and methods present within these published works. You should also be identifying connections, tensions, and contradictions within the already published works of your topic or problem. This involves building on the knowledge of others and understanding what methods, measures, and models we have inherited from previous researchers in our field.

Literature Reviews: Common Errors Made When Conducting a Literature Review [12 min 22 sec]

Video provided courtesy of the Center for Quality Research (CQR)

A literature review helps your reader understand the relationship of your research project to the work of other scholars. It covers the existing knowledge about a problem, and allows you to show the relevance/significance of your contribution to the discussion. Your reader may or may not have read scholarly literature about the theories, methodologies, and literary works you are discussing. But they want to know that you have read it and have thought about it. Your literature review provides not only a summary of the existing scholarship for readers; it also offers your perspective on it.

Begin your work on the literature review by synthesizing the various sources in your annotated bibliography .

For advice on Synthesizing Sources, consider the following from The Purdue Online Writing Lab: [2]

Note that  synthesizing is not the same as summarizing .

• A summary restates the information in one or more sources without providing new insight or reaching new conclusions.
• A synthesis draws on multiple sources to reach a broader conclusion.
• Don’t force a relationship between sources if there isn’t one. Not all of your sources have to complement one another.
• Do your best to highlight the relationships between sources in very clear ways.
• Don’t ignore any outliers in your research. It’s important to take note of every perspective (even those that disagree with your broader conclusions).

Not all humanities research projects contain literature reviews, but many do. Keep in mind that the type of literature review you choose (see list below) pertains to the secondary research – other scholarly sources – and not to the primary literary work. For instance, a literature review about Kate Chopin’s writing will be your thoughts about the scholarship on Chopin and not about Chopin’s text itself. You are summarizing what you see in the scholarly literature about Chopin’s writing. The literature review puts you in the position of authority not just on Chopin’s writing but on the scholarship about her writing. You are seeking to understand what scholars have said about her work. Scholars might belong to different schools of thought (psychoanalytic, feminist, Marxist, etc.). They might make different arguments about Chopin. They might use different methodological approaches. 

If your research involves two or more theories, such as psychology and genre studies, you may need to create multiple literature reviews, one for each theory or methodology. If the theories overlap with each other significantly (i.e., Marxism and Cultural Studies), you may combine them. Your literature review need not include everything about the subject area – you would need to write a book to cover a single theory – but only those concepts and methods that are most relevant to your research problem.

Factors to Consider When Developing Your Literature Review

• Determine the Scope : How broad or narrow should your literature review be? You may want to focus on recent scholarship only, or on a particular school of thought in the literature. Your scope is determined by your purpose; what is it you aim to achieve with your research?
• Establish Criteria : We discussed the importance of defining the purpose and scope of your review on the previous page, but it’s worth reviewing here as well. This step will help you establish important criteria and focus your searching. For example, how many sources will you need? What types of sources (primary, secondary, statistics, media)? Is currency important? Do you know who the prominent authors or theorists are in your subject area? Take some time to map out these or other important factors before you begin searching journals and databases.
• Consider Your Audience : Unlike a work cited page or an annotated bibliography, both of which are lists of sources, a literature review is essayistic and can be considered a precursor to your final paper. Therefore, it should be written in your own voice, and it should be geared toward a specific audience. Considering audience during this early stage will help focus your final paper as well.
• Find Models : We’ll discuss the different types of literature reviews and how to locate examples in the section below. However, even if you’re undecided about what type of review will work best for you, you may want to review some example literature reviews to get a sense of what they look like before you begin your own.

One piece of advice before starting: look for existing literature reviews on your area of scholarship. You can build on the work that other scholars have put into reviewing the scholarly literature. There’s no need to completely “reinvent the wheel” if some of the work is already done.

Scholars sometimes publish “stand-alone” literature reviews that are not part of a larger work; such literature reviews are valuable contributions to the field, as they summarize the state of knowledge for other scholars.

Maria J. Grant and Andrew Booth’s “A Typology of Reviews” identifies 14 distinct types of literature reviews. Further, the UCLA library created a chart to complement the article and for easy comparison of those 14 types of reviews. This section provides a brief summary of the most common literature reviews. For a more complete analysis, please see the full article and the chart .

To choose the most appropriate structure, put yourself in your reader’s shoes and think through their need for information. The literature review is about providing context for your contribution. How much context do people need? Keep it to the minimum necessary; compressing a lot of information into a small amount of text is a must.

These structures are not meant to be straightjackets but tools to help you organize your research. If you find that the tool is working, then keep using it. If not, switch tools or modify the one you are using. Keep in mind that the types of literature reviews are just different ways of organizing information. So, you can discuss literary trends without organizing your review of secondary literature by trend; your discussion can be organized by theory or theme, for examples. In our literature reviews, we are not recounting other scholars’ arguments at length but merely providing key concepts so we can summarize the discussion so far and position our own claims. You don’t have to adhere strictly to one structure or another. They are just organizing tools that help you manage your material (and help your reader make sense of it).

Types of Reviews

• Traditional or narrative reviews : This approach will generate a comprehensive, critical analysis of the published research on your topic. However, rather than merely compiling as many sources as possible, use this approach to establish a theoretical framework for your paper, establish trends, and identify gaps in the research. This process should bring your research question into clearer focus and help define a thesis that you will argue for in your paper. This is perhaps the most common and general type of literature review. The examples listed below are all designed to serve a more specific purpose.
• Argumentative : The purpose of an argumentative literature review is to select sources for the purpose of supporting or refuting a specific claim. While this type of review can help the author make a strong case for or against an issue, they can also be prone to claims of bias. Later in this textbook, we will read about the distinction between warranted and unwarranted bias . One is ok and the other is not.
• Chronological : A chronological review is used when the author wants to demonstrate the progression of how a theory, methodology, or issue has progressed over time. This method is most effective when there is a clear chronological path to the research about a specific historical event or trend as opposed to a more recursive theoretical concept.
• By trend : This is similar to the chronological approach except it focuses on clearly-defined trends rather than date ranges. This would be most appropriate if you want to illustrate changing perspectives or attitudes about a given issue when specific date ranges are less important than the ebb and flow of the trend.
• Thematic : In this type of literature review, the author will select specific themes that he or she feels are important to understanding a larger topic or concept. Then, the author will organize the sources around those themes, which are often based on relevance or importance. The value of this method is that the process of organizing the review by theme is similar to constructing an argument. This can help the author see how resources connect to each other and determine how as well as why specific sources support their thesis.
• Theoretical : The goal of this type of review is to examine how theory has shaped the research on a given topic. It establishes existing theoretical models, their connections, and how extensively they have been developed in the published research. For example, Jada applied critical race theory to her analysis of Sonny’s Blues , but she might also consider conducting a more comprehensive review of other theoretical frameworks such as feminism, Marxism, or postmodernism. Doing so could provide insight into alternate readings, and help her identify theoretical gaps such as unexplored or under-developed approaches to Baldwin’s work.
• Methodological : The approach focuses on the various methodologies used by researchers in a specific area rather than an analysis of their findings. In this case, you would create a framework of approaches to data collection related to your topic or research question. This is perhaps more common in education or the social and hard sciences where published research often includes a methods section, but it is sometimes appropriate for the digital humanities as well.
• Scoping : The aim of a scoping review is to provide a comprehensive overview or map of the published research or evidence related to a research question. This might be considered a prelude to a systematic review that would take the scoping review one step further toward answering a clearly defined research question. See below for more details.
• Systematic : The systematic review is most appropriate when you have a clearly-defined research question and have established criteria for the types of sources you need. In this way, the systematic review is less exploratory than other types of reviews. Rather, it is comprehensive, strategic, and focused on answering a specific research question. For this reason, the systematic review is more common in the health and social sciences, where comprehensiveness is more important. Literature reviews in the Humanities are not usually exhaustive but tend to show only the most representative or salient developments in the scholarship.
• Meta-analysis : Does your research deal with statistics or large amounts of data? If so, then a meta-analysis might be best for you rather than providing a critical review, the meta-analysis will summarize and synthesize the results of numerous studies that involve statistics or data to provide a more comprehensive picture than would be possible from just one study.

An argumentative literature review presents and takes sides in scholarly arguments about the literary work. It makes arguments about other scholars’ work. It does not necessarily involve a claim that the literary work is itself making an argument. Likewise, a chronological literature review presents the scholarly literature in chronological order.

You don’t need to keep strictly to one type. Scholars often combine features from various types of literature reviews. A sample review that combines the follow types –

• Argumentative
• Theoretical
• Methodological

– is the excellent work of Eiranen, Reetta, Mari Hatavara, Ville Kivimäki, Maria Mäkelä & Raisa Maria Toivo (2022) “ Narrative and Experience: Interdisciplinary Methodologies between History and Narratology , ” Scandinavian Journal of History , 47:1, 1-15

When writing your literature review, please follow these pointers:

• Conduct systematic searches
• Use Evidence
• Be Selective
• Use Quotes Sparingly
• Summarize & Synthesize
• Use Caution when Paraphrasing
• Use Your Own Voice

Advice from James Mason University’s “Literature Reviews: An Overview”

A note on synthesizing : Don’t make the common mistake of summarizing individual studies or articles one after the other. The goal is to synthesize — that is, to make observations about groups of studies. Synthesis often uses language like this:

• Much of the literature on [topic x ] focuses on [major themes].
• In recent years, researchers have begun investigating [facets a , b , and c ] of [topic x ].
• The studies in this review of [topic x ] confirm / suggest / call into question / support [idea / practice / finding / method / theory / guideline y ].
• In the reviewed studies [variable x ] was generally associated with higher / lower rates of [outcome y ].
• A limitation of some / most / all of these studies is [ y ].

Please see this sample annotated literature review  from James Mason University.

Structure of a literature review [2]

• Problematization: The 2 to 3 pages of problematization are a distinct, iterative, step. It may take doing such a statement a few times before moving forward to writing the actual paper.
• Search: Write down your keyword sets, your updated keyword sets, and databases. It is perfectly within a reviewer’s rights to ask for these details.
• Summary: Really getting to know major themes requires some annotation of articles. You want to identify core papers and themes and write about them. This helps you really learn the material. [ChatGPT or Wikipedia are no substitute for deep engagement with a paper.]
• Argument: Either outline or create a slide deck that help you express the arguments in your paper. Read them out loud. Have friends look at them. Present them. [Every literature review has an argument. If not, it’s a summary. A summary does not merit publication in a top outlet.]
• Unpacking: Once you’ve nailed the short pitch, unpack the full argument. [ a) Take time in each major section to map out a) the argument, b) the supporting evidence, and the takeaway. b) Take those major sections, reconcile them, make sure they don’t overlap, then move on to writing. c) Sketch out the paper’s sections, tables, figures, and appendices.]
• Writing: Writing is the easy part. You can always put words to the screen. [Revising and improving is hard. Make time to write every day. Improving requires feedback. Find a writing partner to give feedback. Create your tables and figures. Write to them. Make sure the words in the paper align to the visuals.]
• Communicate: When the paper is done, go back and create a paper presentation. [I do this for the papers that I’m most serious about. The act of storyboarding helps me sort out the small pieces of the story that don’t fit together. If I really want it to succeed, I present it. The act of presenting helps me get it right. My best papers sometimes take seven or eight presentations to get it right. Then I return to the paper and fine tune it. Only then, does it have a shot at a top outlet.]

Literature reviews can be published as part of a scholarly article, often after the introduction and sometimes with a header, but they can also be published as a standalone essay. To find examples of what reviews look like in your discipline, choose an appropriate subject database (such as MLA for literary criticism) and conduct a keyword search with the term “Literature Review” added in quotes:

Not only do these examples demonstrate how to structure different types of literature reviews, but some offer insights into trends and directions for future research. In the next section, we’ll take a closer look at some reading strategies to help guide you through this process.

Since scholars already have produced literature reviews on various scholarly conversations, you don’t always need to “reinvent the wheel” (start a literature review from nothing). You can find a published literature review and update it or amend it; scholars do that all the time. However, you must properly cite work you incorporate from others.

• What types of literature review will you be using for your paper? Why did you make this selection over others? If you haven’t made a selection yet, which types are you considering?
• What specific challenges do you face in following a literature review structure?
• If there are any elements of your assignment that need clarification, please list them.
• What was the most important lesson you learned from this page? What point was confusing or difficult to understand?
• In the “Back Matter” of this book, you will find a page titled “Rubrics.” On that page, we provide a rubric for Creating a Literature Review ↵
• Richard West, Brigham Young University, amended by Jason Thatcher, Temple University - https://www.linkedin.com/posts/jason-thatcher-0329764_academicwriting-topten2023-activity-7146507675021766656-BB0O ↵

Writing the Literature Review Copyright © 2021 by Barry Mauer and John Venecek is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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• UNC Libraries
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• ENGL105 - Scholarly Articles 101

Types of Scholarly Articles

Engl105 - scholarly articles 101: types of scholarly articles.

• Peer-review
• Other Types of Sources

Research Articles

Review articles, tips & practice.

• How to Read a Scholarly Article
• Extend Your Knowledge

Sometimes a professor might ask you to find original research or may ask you to not use literature reviews/systematic reviews as sources, but what do those terms mean? How can we tell if our potential source meets our professor's criteria?

In a research article, an original study is conducted by the authors. They collect and analyze data, sharing their methods and results, and then draw conclusions from their analysis. The kind of study performed can vary (surveys, interviews, experiments, etc.), but in all cases, data is analyzed and a new argument is put forth. Research articles are considered primary sources.

• Note: research articles will often contain a section titled "literature review" - this is a section that looks at other existing research as a foundation for their new idea. Simply seeing the words "literature review" does not automatically mean an article is a review article- it is important to look closer

Below is a screenshot of the abstract of the article Effectiveness of Health Coaching in Diabetes Control and Lifestyle Improvement: A Randomized-Controlled Trial , with some words underlined that let us know that a study was conducted and that this is a research article.

A review article gathers multiple research articles on a certain topic, summarizing and analyzing the arguments made in those articles. A review article might highlight patterns or gaps in the research, might show support for existing theories, or suggest new directions for research, but does not conduct original research on a subject. Review articles can be a great place to get an overview of the existing research on a subject. A review article is a secondary source.

• Looking in the reference section of a literature or systematic review can be a good place to find original research studies.

Below is a screenshot of the abstract of the article The Effect of Dietary Glycaemic Index on Glycaemia in Patients with Type 2 Diabetes: A Systematic Review and Meta-Analysis of Randomized Controlled Trials , with words underlined that clue us in that this is a review article.

Tips for identifying article type

Start by looking at the abstract to determine if a source might be a research article or a review article. If you're not sure after looking at the abstract, find the methods section for the source - what methods did the authors use? If they mention searching databases, it's most likely a review and if they mention conducting an experiment, survey, interview, etc., it's most likely a research article. If you're still unsure, feel free to reach out to a librarian and ask ! 

Let's Practice

Below are two different scholarly articles. Look at the abstract and the methods section- Which one is an original research study? Which one is a literature review?

• Article 1- Research or Review?
• Article 2- Research or Review?

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Evidence Synthesis Guide : Review Types & Decision Tree

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Common Types of Evidence Synthesis

See  Right Review   for descriptions of additional quantitative and qualitative review types.  

​​Systematic Review

• A methodical and comprehensive literature synthesis focused on a well-formulated research question.
• Compares, evaluates, and synthesizes published and unpublished evidence in a search for the effect of an intervention.
• Designed for high sensitivity; commonly producing a large number of search results.
• Time-intensive and often take months to a year or more to complete. 
• The most commonly referred to type of evidence synthesis. Sometimes confused as a blanket term for other types of reviews.  

Meta-analysis

• Statistical technique for combining the findings from disparate quantitative studies.
• Uses statistical methods to objectively evaluate, synthesize, and summarize results.
• May be conducted independently or as part of a systematic review.  

​Scoping Review or Evidence Map

• Systematically and transparently collect and categorize existing evidence on a broad question of scientific, policy or management importance.
• Seeks to identify research gaps and opportunities for evidence synthesis rather than searching for the effect of an intervention. 
• May critically evaluate existing evidence, but does not attempt to synthesize the results in the way a systematic review would. 
• May take longer than a systematic review.  

​Rapid Review

• Applies Systematic Review methodology within a time-constrained setting.
• Employs methodological "shortcuts" (limiting search terms for example) at the risk of introducing bias.
• Useful for addressing issues needing quick decisions, such as developing policy recommendations.  

Umbrella Review

• Reviews other systematic reviews on a topic. 
• Often defines a broader question than is typical of a traditional systematic review.
• Most useful when there are competing interventions to consider.

Literature (Narrative) Review

• A broad term referring to reviews with a wide scope and non-standardized methodology. 
• Aim is specificity; search results are not comprehensive and are narrowly focused on the topic.
• Search strategies, comprehensiveness, and time range covered will vary and do not follow an established protocol.

The descriptions and decision tree presented further below are based on content developed by Cornell University Library . 

Review Type Decision Tree

Use the decision tree to determine which type of evidence synthesis review works best for you depending on your team, time, research question, and resources.  

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• Case Report
• Open access
• Published: 13 August 2024

Pathological findings in enucleated eyes of patients with neurofibromatosis type 1: report of a case with 15-year follow-up and review of 14 patients in the literature

• Toshihiko Matsuo 1 , 2 , 6 ,
• Kenji Nishida 3 ,
• Takehiro Tanaka 3 ,
• Takaya Seno 4 ,
• Kiyoshi Yamada 4 &
• Shigeki Ono 5  

BMC Ophthalmology volume  24 , Article number:  341 ( 2024 ) Cite this article

46 Accesses

Metrics details

Backgrounds

Iris nodules are frequently noted as clinical manifestations of neurofibromatosis type 1 but the other intraocular manifestations are rare. The purpose of this study is to present a patient with a phthisic eye who underwent enucleation for a cosmetic reason after 15-year follow-up and also to review 14 patients with enucleation described in the literature.

Case presentation

A 17-year-old man with neurofibromatosis type 1 from infancy underwent the enucleation of phthisic left eye and also had the resection of eyelid subcutaneous mass lesions on the left side for a cosmetic reason. He had undergone four-time preceding surgeries for eyelid and orbital mass reduction on the left side in childhood and had developed total retinal detachment 10 years previously. Pathologically, the enucleated eye showed massive retinal gliosis positive for both S-100 and glial fibrillary acidic protein (GFAP) in the area with involvement of the detached retinal neuronal layer, together with a more fibrotic lesion along the choroid which were, in contrast, negative for both S-100 and GFAP. The choroid, ciliary body, and iris did not show apparent neurofibroma while episcleral neurofibroma was present.

Literature review

In review of enucleated eyes of 14 patients in the literature, buphthalmic eyes with early-onset glaucoma on the unilateral side was clinically diagnosed in 9 patients who frequently showed varying extent of hemifacial neurofibromatosis which involved the eyelid and orbit on the same side. Pathologically, neurofibromas in varying extent were found in the choroid of 12 patients. One patient showed choroidal malignant melanoma on the left side and fusiform enlargement of the optic nerve on the right side suspected of optic nerve glioma. The phthisic eye in another patient showed massive retinal gliosis similar to the present patient.

Conclusions

In summary of the 15 patients with neurofibromatosis type 1, including the present patient, buphthalmic or phthisic eyes with no vision were enucleated for cosmetic reasons and showed choroidal neurofibroma in most patients and massive retinal gliosis in two patients including the present patient.

Peer Review reports

Neurofibromatosis type 1 is characterized by typical skin lesions such as café-au-lait spots and nodular lesions. [ 1 , 2 ] As one of phacomatoses which show other-organ manifestations in addition to typical skin lesions, neurofibromatosis type 1 shows Lisch iris nodules in ophthalmic examinations as well-known frequent manifestations in the other organs. [ 3 , 4 , 5 , 6 , 7 , 8 ] Cranial and facial bone defect is also encountered as a rare presentation. Neurofibromatosis type 1 is caused by mutations in the gene NF1 which encodes neurofibromin and plays a role in the regulation of cell proliferation. [ 9 ] The absence of neurofibromin or the presence of malfunctioning protein is considered to lead to the proliferation of neurofibroma cells. In the consequences, optic nerve glioma, malignant and benign peripheral nerve sheath tumors, and gastrointestinal stromal tumor are described to develop in patients with neurofibromatosis type 1. [ 2 ] Neurofibromatosis type 2 is a different disease entity which is famous for bilateral acoustic (vestibular) nerve schwannoma and is caused by mutations in a different gene, NF2 which encodes merlin. [ 10 , 11 ]

In this study, we presented an adolescent patient with neurofibromatosis type 1 who underwent enucleation of the phthisic eye and resection of eyelid and orbital neurofibroma lesions on the same side as a cosmetic reason in the 15-year follow-up from the infancy. We showed pathological findings of the phthisic eye in the present patient and also reviewed pathological descriptions of enucleated eyes in 14 patients with neurofibromatosis type 1 in the literature. [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]

A 3-year-old boy with the diagnosis of neurofibromatosis type 1 (von Recklinghausen disease) was referred for ophthalmic evaluation during the hospitalization for left orbital mass reduction surgery by orbitozygomatic approach. The visual acuity in decimals with both eyes open was 0.4. He was scared when his right eye was covered, suggestive of poor vision in the left eye. The right eye appeared normal. He had blepharoptosis and proptosis with downward shift of the eye on the left side. The bulbar conjunctiva was edematous and the optic nerve was atrophic in the left eye. He showed eye movement with limitations on the left side. In the past history, he was diagnosed as neurofibromatosis type 1 by many café-au-lait spots of the systemic skin and underwent upper eyelid mass resection on the left side at the age of 1.5 years at a different hospital (Fig.  1 A, B, C and D).

Axial views of computed tomographic scan ( A , B ) and T2-weighted axial views of magnetic resonance imaging ( C , D ) at the age of 1 year. Note subcutaneous eyelid lesions and orbital lesions on the left side, together with posterior orbital wall defect (arrow in A) and brain parenchymal anomalies of the temporal lobe (arrows in C, D). Axial views of magnetic resonance imaging at 7.5 years (E, T1-weighted image; F, T2-weighted image) and at 8 years (G, T1-weighted image; H, T2-weighted image). Note funnel-shaped total retinal detachment in the left eye (arrows in G, H) which was absent half a year previously ( E , F )

At the age of 5 and 6 years, he underwent three surgeries for orbital mass extirpation on the left side and cranial base reconstruction with titan mesh implantation. At the age of 7 years when he was referred for ophthalmic examinations, the best-corrected visual acuity in decimals was 1.2 in the right eye and 0.02 in the left eye. The intraocular pressure was 16 mmHg in the right eye and 23 mmHg in the left eye. The right eye was normal except for small iris nodules. He showed mydriasis (Fig.  2 A) with sluggish light reflex in the left eye. He had lower bulbar conjunctival edema (Fig.  2 B), iris nodules (arrow in Fig.  2 A), and optic disc atrophy in the left eye. He started to have 0.005% latanoprost eye drops once daily in the left eye. In half a year, he began to show anterior and posterior subcapsular cataract in the left eye (Fig. 2 C and D). The intraocular pressure was 15 mmHg in the left eye with latanoprost eye drops. He showed no retinal detachment at that time (Fig.  1 E and F). Further half a year later at 8 years old, he showed mature cataract (Fig.  2 E and F) in the left eye and ultrasound examination disclosed total retinal detachment in a closed funnel shape (Fig.  2 G). Magnetic resonance imaging also showed total retinal detachment in the left eye (arrows in Fig.  1 G and H). The left eye became phthisic in a year. He was followed once a year afterwards. At 11 years old, he showed subconjunctival mass lesion in the lower bulbar edematous conjunctiva on the left side (Fig.  2 H) which remained stationary for a few years (Fig.  2 I).

Slit-lamp photographs in the left eye at the age of 7 years ( A , B ), showing many iris nodules (arrow in A) and lower bulbar conjunctival lesion (arrow in B). Slit-lamp photographs in the left eye at 7.5 years ( C , D ), showing mild anterior subcapsular cataract which allows the visualization of fundus to prove no retinal detachment (Fig.  1 E and F). Slit-lamp photographs ( E , F ) and ultrasonography ( G ) in the left eye at 8 years, showing mature cataract ( E , F ) and funnel-shaped total retinal detachment ( G ). Note many iris nodules (arrow in E). Slit-lamp photographs in the left eye at 11.5 years ( H ) and at 13.5 years ( I ), showing phthisic eye and enlarging lower bulbar conjunctival lesion (arrows in H, I)

At 17 years old, he and his family wished to plan a cosmetic surgery before he would graduate from a high school. Computed tomographic scan showed the defective posterior bony orbital wall to the brain parenchyma on the left side (Fig.  3 A) with the main mass lesion in the upper eyelid and the downwardly displaced phthisic eye ball (Fig.  3 B) on the left side as well as lateral ventricular dilation on both sides (Fig.  3 C). Magnetic resonance imaging demonstrated the bulged subdural space with arachnoid fluid collection toward the orbital space on the left side (Fig.  3 D and E). The entire orbit and subcutaneous area of the upper eyelid on the left side was occupied with mass lesions and the phthisic eye ball was displaced downwardly. The subconjunctival mass lesion was visible on the lower bulbar conjunctiva (Fig.  3 H). The visual acuity in the left eye was no light perception. He was healthy and the physical examinations detected no particular findings. Blood examinations including complete blood cell counts, blood glucose, electrolytes, liver and kidney function tests were all within the normal limits. Urinalysis was also normal. He started to take oral selumetinib (MEK1/2 inhibitor) 80 mg daily.

Axial views of computed tomographic scan at the age of 17 years ( A , B , C ), showing posterior orbital bone defect (arrow in A) with upper eyelid and orbital mass lesion on the left side, inferiorly dislocated phthisic left eye ( B ), and dilated lateral ventricles ( C ). T2-weighted axial views of magnetic resonance imaging at 17 years ( D , E ), showing upper eyelid mass lesion (arrow in D) and phthisic left eye (arrow in E) with temporal lobe brain parenchymal atrophy on the left side. Slit-lamp photograph half a year later just before the surgery ( H ), showing phthisic left eye and lower bulbar conjunctival lesion (arrow in H). Macroscopic photographs of enucleated left eye (F, cornea with arrow) and its cut surface (G, optic nerve with arrow), showing total retinal detachment with white tissue filled in the totally detached retinal funnel. Superior to inferior vertical section of optical coherence tomography (I), slit-lamp photograph ( J ), and wide-field fundus photograph ( K ) in the right eye at the age of 18 years after the surgery. Note iris nodules (arrows in J) and a suspected choroidal nodule (arrows in I, K) in the right eye

Half a year later, he underwent enucleation of the phthisic left eye ball and extirpation of the subcutaneous mass lesion together with upper eyelid skin resection. The enucleation was done at first by circumferential cutting of the conjunctiva at the corneal limbus. The sclera and four rectus extraocular muscles showed firm adhesion with the surrounding tissues probably of neurofibromatous lesions. After the blunt dissection of the surrounding tissues which adhered firmly to the sclera and 4 rectus extraocular muscles, the eye ball was extirpated by cutting the 4 rectus muscles at the insertion and then by cutting the optic nerve. The conjunctiva was sutured to make the sac for future insertion of a prosthesis. The skin of the upper eyelid was resected in a crescent shape by an incision line below the eye brow to the lateral side, [ 26 ] and the mass was carefully dissected from the pulsating and bulging interface to the presumed dura of the brain. The skin incision was sutured tightly to lift the canthal line on the left side in alignment with the right eye. He showed no operative or postoperative complications. The best-corrected visual acuity in the right eye was 1.2. The right eye showed small iris nodules (arrows in Fig.  3 J) and the normal macular structure (Fig.  3 I) with a suspected small choroidal nodule (Fig.  3 K). The left conjunctival sac was fitted with a prosthetic eye. Family history for neurofibromatosis type 1 was absent. He and his family did not want a genetic testing for NF1 .

Pathological findings of the case

The resected orbital and eyelid lesions showed spindle cells with ovoid nuclei and ill-defined eosinophilic cytoplasm which were distributed in diffuse pattern (Fig.  4 A and B). Mitotic cells or cells with aberrant nuclei were absent. The spindle cells were positive for S-100 (Fig.  4 C) and CD34 (Fig.  4 D), and negative for glial fibrillary acidic protein (GFAP, Fig.  4 E). All the features were consistent with the diagnosis of neurofibroma.

Subcutaneous left eyelid and orbital mass. Spindle-shaped cells with no aberrant nuclei and ill-defined eosinophilic cytoplasm arranged in diffuse pattern by hematoxylin-eosin stain ( A , B ). Spindle-shaped cells are positive for S-100 ( C ) and CD34 ( D ), negative for glial fibrillary acidic protein (GFAP) ( E ), consistent with the diagnosis of neurofibroma. Bar = 500 μm in A, and 50 μm in B-E

The phthisic left eye was enucleated with the intact sclera (Fig.  3 F). Macroscopic view of a section of the fixed eye ball showed total retinal detachment in a funnel shape which was filled with white tissue from the optic disc to the posterior border of the calcified lens (Fig.  3 G). In hematoxylin-eosin stains, no apparent neurofibroma was noted in the iris, ciliary body (Fig.  5 A and B), and choroid (Fig.  5 C) while neurofibroma was observed in close contact with the sclera in the episcleral location (Fig.  5 B). The neuronal layers of the original retina were observed in a swirling pattern inside the cellular mass which was formed by total retinal detachment (Fig.  5 C). The cellular mass of the totally detached retina was fully positive for GFAP (Fig.  6 B) while the part of the mass in proximity to the optic nerve was positive for S-100 (Fig.  6 C). The other part of the intraocular mass along the choroid appeared more fibrotic (Fig.  6 A) and was negative for GFAP (Fig.  6 B) and S-100 (Fig.  6 C).

Sections of phthisic left eye. No apparent neurofibroma in iris (arrows in A , B ) and ciliary body (black asterisks in A, B). Calcified lens (yellow asterisks in A, B) and episcleral neurofibroma (arrowheads in B). A cellular mass lesion involving the swirling detached retina with residual retinal neuronal layers (arrowheads in C). Hematoxylin-eosin stain. Bar = 1000 μm in A and B, and 500 μm in C

Intraocular mass lesion adjacent to optic nerve (arrow in A ) in hematoxylin-eosin stain, positive for glial fibrillary acidic protein (GFAP) ( B ) and S-100 ( C ). There is another fibrotic mass lesion along the choroid (asterisks in A, B, C) negative for GFAP (B) and S-100 (C). The optic nerve (arrows in A, B, C) is positive for GFAP (B) and S-100 (C). Bar = 1000 μm in A, B, and C

Methods of literature review

To analyze similar cases, PubMed and Google Scholar were searched with key words, “neurofibromatosis”, “eye” and “enucleation”. Old literature was collected from references cited in the articles identified during the literature search. The bibliographic database of medical literature in Japanese (Igaku Chuo Zasshi, Ichushi-Web), published by the Japan Medical Abstracts Society (JAMAS, Tokyo, Japan), was also searched with the same key words to get no relevant literature. A sufficient description was found in 14 patients with neurofibromatosis type 1 (Table  1 ). [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]

Results of literature review

The 15 patients with neurofibromatosis type 1 (Table  1 ), including the present patient, who had pathological examinations of the enucleated eye, were 10 males and 5 females with the age at surgery or autopsy ranging from 1 to 56 (median, 18) years (Table  1 ). The eye was examined at autopsy in 2 patients (Case 1 and 4) and the other 13 patients underwent enucleation of buphthalmic eyes or phthisic eyes (Case 14, 15) or normally appearing eyes (Case 7, 10) with no vision. One patient (Case 11) lost vision by retinal detachment in the background of choroidal malignant melanoma. Glaucoma of early onset, namely, congenital glaucoma, on the unilateral side was diagnosed in 9 patients. The varying extent of hemifacial neurofibromatosis was observed to involve the eyelid and orbit in 10 patients which roughly overlapped with 9 patients with early-onset glaucoma except for one who lost vision probably by compression optic neuropathy with the orbital mass (Case 7). Systemically, café-au-lait spots were described in 10 patients, multiple skin nodules in 3, and tibial fibrous dysplasia in one (Case 6). The positive family history for neurofibromatosis type 1 was described in 3 patients (Case 11, 12, 14).

Pathologically, neurofibromas in varying extent were found in the choroid of 12 patients. One patient (Case 11) showed choroidal malignant melanoma on the left side and fusiform enlargement of the optic nerve on the right side suspected of optic nerve glioma. In this patient, multiple melanocytic hamartomas were observed in the choroid of the enucleated eye with malignant melanoma. The phthisic eyes in the remaining 2 patients including the present patient (Case 14, 15) showed massive retinal gliosis. Neurofibroma in inferior rectus muscle was described in 2 patients (Case 7, 8).

The present patient showed typical features of neurofibromatosis type 1 from birth such as café-au-lait spots and hypertrophic thickened upper eyelid on the left side caused by orbital and eyelid neurofibroma. He was followed by the team of a plastic surgeon, neurosurgeon, and ophthalmologist. The plastic surgeon and neurosurgeon did volume reduction surgeries for orbital and upper eyelid neurofibroma for cosmetic reasons. The vision in the left eye appeared to be poor in childhood due to compression optic neuropathy with orbital neurofibroma. In ophthalmic examinations, he was checked to have normal vision in the right eye and stable condition of the left eye with poor vision. He had no signs of congenital glaucoma: the intraocular pressure in both eyes was within the normal range, and iris ectropion, as a sign of congenital glaucoma in patients with neurofibromatosis type 1, [ 27 ] was not noted by slit-lamp examinations in the follow-up.

In the process of 15-year follow-up, he was found to develop mature cataract and total retinal detachment in the left eye at the age of 8 years on the semiannual visit half a year after the previous visit. He did not notice any symptoms in regard to this abrupt change in the left eye. At that time, the reason for the retinal detachment remained basically unknown and would be attributed to incidental blunt trauma to the deviated eye or to suspected intraocular proliferation of neurofibroma. The surgery for the retinal detachment was not recommended because of rather old total retinal detachment in a closed-funnel shape which was revealed by the ultrasound examination. The pathological examinations of the phthisic eye which was enucleated almost 10 years after the development of total retinal detachment showed a mass lesion of massive retinal gliosis [ 28 ] involving the detached retina.

Massive retinal gliosis is a concept to show non-neoplastic retinal glial proliferation. [ 28 ] Massive retinal gliosis has been described in a case as sequelae to retinal detachment surgery. [ 29 ] In another case with the age at 22 months, total retinal detachment has been described in the background of neurofibromatosis type 1. [ 30 ] In the present patient, the intraocular mass consisted of two areas from the viewpoint of immunohistochemistry. One area with involvement of the swirled detached retinal tissue was positive for both S-100 and GFAP while the other area along the choroid was negative for both S-100 and GFAP. The area positive for S-100 and GFAP is designated as massive retinal gliosis while the other area negative for S-100 and GFAP is a fibrotic tissue which would be formed by metaplastic retinal pigment epithelial cells or choroidal fibroblasts.

In the enucleated eye of the present patient, no apparent iris, ciliary body or choroidal neurofibromas were found pathologically. The iris ectropion was absent. [ 27 ] The episcleral neurofibroma in the patient would be the extension of orbital neurofibromatous lesions which surrounded the enucleated eye ball. The patient did show iris nodules on clinical examinations many years previously when the clear cornea allowed the visualization. The iris nodules would become atrophic in the many-year process of phthisis bulbi. On the visit after the recent surgery, he showed iris nodules as well as a suspected choroidal nodule in the right eye. In the review of other enucleated eyes in patients with neurofibromatosis type 1 which were reported in the literature, choroidal, ciliary body, and iris nodules were most frequent pathological findings (Table  1 ).

In the review of enucleated eyes in the literature (Table  1 ), most patients were described to have congenital glaucoma in the unilateral eye, together with the hemifacial lesion which manifested as eyelid or orbital lesion or both lesions of neurofibromatosis on the same side. Their eyes became buphthalmic and painful and lost the vision, leading thus to the enucleation. Most of the enucleated eyes showed choroidal, iris, and ciliary body neurofibroma which would underlie the obstruction of aqueous humor outflow pathway in the iridocorneal angle of the eye. In contrast, the present patient did not develop a buphthalmic eye and he appeared to lose the vision by compression optic neuropathy by the orbital mass lesion with neurofibromatosis. He did show mild increase of intraocular pressure up to 23 mmHg in the left eye when he had already developed optic nerve atrophy. The enucleation of phthisic eye was described only in one patient with neurofibromatosis type 1 (Case 14) in the literature, [ 25 ] in addition to the present patient. These 2 patients showed massive retinal gliosis with total retinal detachment as a common pathological feature, suggesting that the phthisis with total retinal detachment would be the background for this pathological presentation.

Data availability

No datasets were generated or analysed during the current study.

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Acknowledgements

The authors receive no financial support for the research, authorship, and/or publication of this article.

Author information

Authors and affiliations.

Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University, Okayama City, 700-8558, Japan

Toshihiko Matsuo

Department of Ophthalmology, Okayama University Hospital, Okayama City, 700-8558, Japan

Department of Pathology, Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Okayama City, 700-8558, Japan

Kenji Nishida & Takehiro Tanaka

Department of Plastic and Reconstructive Surgery, Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Okayama City, 700-8558, Japan

Takaya Seno & Kiyoshi Yamada

Department of Neurological Surgery, General Medical Center, Kawasaki Medical School, Okayama City, 700-8505, Japan

Shigeki Ono

Regenerative and Reconstructive Medicine (Ophthalmology), Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University, Shikata-cho 2-5-1, Okayama City, 700-8558, Japan

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T.M., as an ophthalmologist, followed the patient and did surgery, and wrote the manuscript. K.N. and T.T., as pathologists, made pathological diagnosis. T.S. and K.Y., as plastic surgeons, and S.O., as a neurosurgeon, followed the patient and did surgery. All authors approved the final version of the manuscript.

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Correspondence to Toshihiko Matsuo .

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Matsuo, T., Nishida, K., Tanaka, T. et al. Pathological findings in enucleated eyes of patients with neurofibromatosis type 1: report of a case with 15-year follow-up and review of 14 patients in the literature. BMC Ophthalmol 24 , 341 (2024). https://doi.org/10.1186/s12886-024-03604-5

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The role of circular RNAs (circRNAs) as a prognostic factor in lung cancer: a meta-analysis

• Sanabil Ahsan 1 , 2 ,
• Thin Thin Win 3 ,
• Saint Nway Aye 3 &
• Nan Nitra Than 4  

BMC Cancer volume  24 , Article number:  988 ( 2024 ) Cite this article

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Lung cancer is a leading cause of cancer-related death worldwide. Among various histological types of lung cancer, majority are non-small cell lung cancer (NSCLC) which account for > 80%. Circular RNAs (circRNAs) are widely expressed in various cancers including lung cancer and implicated in tumourigenesis and cancer progression. This study aimed to systematically evaluate the prognostic values of circRNAs in lung cancer.

A systematic literature search was done in PubMed, Embase, and MEDLINE databases to select the eligible studies which reported the association between the expression of circRNAs and overall survival (OS) or disease-free survival (DFS) in histopathologically diagnosed lung cancer patients. The pooled hazard ratio (HR) and 95% confidence interval (CI) were assessed to determine the prognostic significance of circRNAs.

A total of 43 studies were eligible for this meta-analysis (MA). 39 different types of circRNAs were reported: 28 showing upregulating and 11 showing downregulating action in lung cancer. High expression of circRNAs with upregulating action in lung cancer was associated with worse prognosis and poor OS (HR 1.93, 95% CI [1.61–2.33], p  < 0.00001). High expression of circRNAs with downregulating action in lung cancer was associated with favorable OS and prognosis (HR 0.73, 95% CI [0.58–0.94], p  = 0.01). However, there was no statistically significant association between high and low expression of both upregulating and downregulating circRNAs and DFS (HR 1.44, 95% CI [0.92–2.24], p  = 0.11).

Conclusions

This MA confirmed the pivotal role of circRNAs as important prognostic biomarkers for lung cancer, especially NSCLC. High expression of upregulating circRNAs is associated with poor prognosis; however, high expression of downregulating circRNAs is associated with favorable prognosis. Therefore, downregulatory action of circRNAs should be considered a promising treatment in the management of lung cancer, especially NSCLC.

Peer Review reports

Introduction

Lung cancer is a leading cause of cancer-related death in both men and women [ 1 ]. >80% of lung cancers are non-small cell lung cancer (NSCLC) and only 13% are small cell lung cancer (SCLC) [ 2 ]. Generally, the prognosis of lung cancer especially NSCLC is mainly based on the tumor-node-metastasis (TNM) staging [ 2 ], histopathological types [ 2 ], and predictive biomarker analyses, such as epidermal growth factor (EGFR) mutation [ 3 ], anaplastic lymphoma kinase (ALK) translocations [ 4 ] and BRAF mutation [ 5 ]. However, the prognosis varies significantly even among the patients with the same TNM staging, histomorphological characteristics, and mutation status [ 6 ].

In cancer management, diagnostic and prognostic biomarkers with high sensitivity and specificity play a crucial role in preventing or treating cancer. Circular RNAs (circRNAs) which are abundant in serum, plasma, and other body fluids with stable property and high specificity has been described as molecular marker in the initiation and development of cancer [ 7 , 8 ].

In recent years, circRNAs have been recognized as a new sensitive, non-invasive biomarker for diagnosis, prognosis and even prediction to therapeutic responses in many types of cancer including lung cancer [ 9 ]. Few meta-analyses (MAs) were done to assess the role of circRNAs in lung cancer. However, they were only focused on NSCLC and not on different histopathological types of lung cancer [ 10 , 11 ]. Therefore, we aimed to conduct this updated MA which includes the latest primary studies to synthesize the evidence on the role of circRNAs as a prognostic factor in all histopathological types of lung cancer.

Materials and methods

The systematic review (SR) and MA were done according to the updated guideline of the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) statement [ 12 ].

Identification of eligible studies

The systematic literature search was carried out in health-related electronic databases such as PubMed, Embase and MEDLINE. The search terms used were “circular RNAs/circRNAs, lung cancer, non-small cell lung cancer, small cell lung cancer and prognosis”. The search was limited to original articles published in the English language up to July 2023. To find additional studies, reference lists of the original articles were also screened.

Inclusion and exclusion criteria

Studies selection was based on criteria of PICOTS format: (1) Participants (P): All patients who have been histopathologically diagnosed with non-small cell and small cell lung cancer; (2) Index prognostic factor (I): circRNAs; (3) Comparisons (C): Not applicable to this review; (4) Outcomes (O): Outcomes were overall survival (OS) which is defined as the length of time that patients remained alive after diagnosis of cancer; and disease progression-free survival (DFS) which is defined as the length of time that patients remained disease‐free/cancer-free; (5) Setting (S): Hospital/Pathology laboratory [ 13 ]. Review articles, case reports, editorials, letters, commentaries, and articles in non-English languages were excluded from this MA.

Literature search and study selection

Two researchers (TTW, SA) conducted an independent literature search in healthcare electronic databases (PubMed, Embase and MEDLINE). Any disagreements between both researchers were initially discussed between two researchers. If an agreement was not reached, two researchers discussed with a third researcher (SNA) to finalize. The articles were screened according to the PRISMA flowchart as displayed in Fig.  1 . The articles that did not fit the inclusion criteria based on abstract and title alone were excluded. Finally, full-text articles were examined to obtain the included studies required for MA.

PRISMA flowchart summarizing the process to identify the eligible studies

Assessment of study quality

The quality of eligible studies was assessed by the Newcastle-Ottawa Quality Assessment Scale (NOS) [ 14 ]. Studies were assessed using three categories, selection of study groups (0–4 points), comparability (0–2 points), and exposure (0–3 points). A total score ≤ of 3 was considered low quality, scores between 4 and 6 were moderate quality and scores ≥ 7 were high quality. These scores were used only to facilitate the interpretation of the MA results, but not used as a criterion for inclusion or exclusion of the studies. During these processes, any discrepancy or disagreement was resolved by discussion among authors to arrive at a consensus.

Data extraction

Two researchers (TTW, SA) independently extracted the relevant data from the included studies using a piloted data extraction sheet. Discrepancies were discussed thoroughly and finalized with a third researcher (SNA). The data that were extracted included study title, first author with year of publication, country of publication, histopathological type of lung cancer, type of circRNA, OS and DFS with hazard ratio (HR), [95% confidence interval (CI)], and p-value.

Statistical analysis

The outcome analyses of OS and PFS were estimated as HR for the prognostic value of circRNAs in patients with lung cancers. From the statistical analysis, heterogeneities were assessed using I 2 statistics. To avoid heterogeneity, if the I 2 statistic is more than 50%, a random effects model was used; and if the I 2 statistic is less than 50%, a fixed effect model was used. A two-tailed p-value of less than 0.05 was considered statistically significant. The corresponding 95% CI was used to quantify the precision of the estimated HR. MA was performed with Review Manager (RevMan 5.4) software.

Literature search results

A total of 2137 potential studies were identified using the preliminary search strategy; 804 were from PubMed, 731 were from EMBASE, and 603 were from MEDLINE. A total of 1873 studies which included duplicates, review articles and irrelevant studies were removed in the screening stage. Based on the title and abstracts, 202 studies were removed. After that, the full texts of 63 studies were reviewed. 20 studies were excluded due to wrong outcomes, wrong study design, or no reported HR and 95% CI. Finally, 43 studies were included for SR and MA. A three-phase flow chart of the study selection process based on the updated PRISMA statement 2020 is illustrated in Fig.  1 .

Characteristics of the included studies

The characteristics of the 43 included studies are shown in Table  1 . All the included studies were carried out in China. There were 39 different types of circRNAs. Among them, Cirs-7 was reported by 3 studies [ 34 , 39 , 41 ], Circ_0020123 was reported by 2 studies [ 33 , 35 ] and Circ_0067934 was reported by 2 studies [ 36 , 46 ]. 28 different types of cirRNAs (Circ_0003645, CircUSP7, Circ_001569, Circ_0128332, Circ_0074027, Circ-BANP, Circ-RAD23B, CircATXN7, CircRARS, Circ_000984, Circ_0016760, Circ-FOXM1, CircRNA_103809, CircSWT1, Circ_0001715, Circ_0007534, CircPVT1, CircPRKCI, Circ_0020123, CiRS-7, Circ_0067934, CircVANGL1, Circ-PRMT5, Circ_0001946, Circ_0023179, Circ_101237, CircFADS2 and Circ_102231) showed upregulating action in the lung cancer and 11 different types of circRNAs (Circ_100395, Circ_0065214, CESRP1, Circ-ITCH, Circ_0001649, Circ_11780, Circ-SMARCA5, CircCRIM1, Circ_0046264, Circ_0006427 and Circ_007230) showed downregulating action in the lung cancer. 32 studies [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 ] reported that high expression of circRNAs was associated with unfavorable prognosis and facilitated the tumour progression (upregulation). The remaining 11 studies [ 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 ] reported that high expression of circRNAs was associated with favorable prognosis by inhibiting tumour progression (downregulation) in lung cancer. Among 43 studies, a majority of the studies reported on NSCLC; 32 studies [ 15 , 16 , 17 , 19 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 30 , 31 , 33 , 34 , 35 , 36 , 38 , 39 , 41 , 42 , 43 , 44 , 46 , 47 , 48 , 50 , 51 , 52 , 53 , 57 ] on NSCLC, 2 studies [ 20 , 55 ] on just lung cancer without specific histopathological types, 8 studies on adenocarcinoma [ 18 , 29 , 32 , 37 , 40 , 45 , 54 , 56 ], and only one study on SCLC [ 49 ]. All 43 studies reported OS with HR and 95% CI. Only 5 studies [ 24 , 28 , 39 , 43 , 53 ] reported DFS with HR and 95% CI.

Methodological quality of the included studies and publication bias

Based on the NOS assessment of the methodological quality of the included studies, the scores of all 43 included studies ranged from 6 to 9. Therefore, all included studies in this MA showed high quality. Publication bias was assessed for all included studies. Funnel plots of Begg’s and Egger’s tests for the publication bias of upregulated and downregulated circRNAs are shown in Figures S1 and S2 .

Prognostic value of circRNAs on OS and DFS in lung cancers

As 32 studies [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ] reported circRNAs that were upregulating in lung cancer and only 11 studies [ 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 ] reported circRNAs that were downregulating in lung cancer, we meta-analyzed these two groups of circRNAs separately. MA of upregulating circRNAs showed a favorable OS with low expression compared to high expression (HR 1.93, 95% CI [1.61–2.33], p  < 0.00001); and heterogeneity I 2 was 76% (Fig.  2 ). MA of downregulating circRNAs showed a favorable OS with high expression compared to low expression (HR 0.73, 95% CI [0.58–0.94], p  = 0.01); and heterogeneity I 2 was 54% (Fig.  3 ).

Forest plot of the association between high and low expression of upregulating CircRNAs and overall survival of lung cancer

Forest plot of the association between high and low expression of downregulating CircRNAs and overall survival of lung cancer

As only 4 studies [ 24 , 28 , 39 , 43 ] reported DFS in association with expression of upregulating and only one study [ 53 ] reported downregulating cirRNAs respectively, MA was done all together for those 5 studies. There was no significant association between DFS and expression of circRNAs (HR 1.44, 95% CI [0.92–2.24], p  = 0.11); heterogeneity I 2 was 90% (Fig.  4 ).

Forest plot of the association between high and low expression of CircRNAs and disease-free survival of NSCLC

CircRNAs are known to have a diverse array of functions. They act as miRNA sponges, interact with RNA-binding proteins (RBPs), regulate alternative splicing and transcription, facilitate translation, generate pseudogenes, transport molecules, and mediate cell-to-cell communication [ 58 , 59 ]. Characterized by their unique covalently closed loop structures, circRNAs are involved in the regulation of gene expression and are emerging as key players in the oncogenic process [ 60 ]. They have also emerged as a large class of primarily non-coding RNA molecules, many of which have key roles in cancer development and progression through diverse mechanisms of action [ 61 ]. Thus, they were reported as promising biomarkers for cancer diagnosis and prognostication as well as for early cancer detection and therapeutic targets or agents to inhibit oncogenic microRNAs or proteins [ 59 , 62 ]. In recent years, an increasing number of studies have shown that some circRNAs have a significant association with the prognosis and progression of cancer; and they are aberrantly expressed in lung cancer, especially NSCLC [ 63 , 64 ]. In the oncogenic process of NSCLC, circRNAs contribute to cancer proliferation and invasion by sponging specific miRNAs, impacting crucial oncogenic pathways [ 63 , 65 ].

Upregulating circRNAs play roles in proliferation, migration, invasion, apoptosis, cell cycle, stemness of lung cancer stem cells, chemotherapy resistance, tumor metabolism, tumor microenvironment (TME), and immune evasion of lung cancer cells [ 66 ]. Most of the upregulating circRNAs promoted the activation of nuclear factor kappa-B (NF-kB) regulatory signaling, epidermal growth factor receptor (EGFR), cyclin E1 (CCNE1) and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit delta (PIK3CD); and thus, exerted remarkable effects through sponging miR-7 [ 34 , 39 , 41 ]. Therefore, cancers that highly express those upregulating circRNAs are associated with a poor prognosis due to rapid tumour invasion, tumour proliferation and chemoresistance.

Some researchers have reported MA on the prognosis of NSCLC in association with various types of circRNAs. The first MA was done in 2019 and it was found that both upregulating and downregulating circRNAs are associated with a poor prognosis of lung cancer [ 67 ]. Later, another MA reported that expression of upregulating circRNAs was significantly associated with a poor prognosis for NSCLC [ 68 ].

In our MA, we collected 43 primary studies that reported an association between the expression of 39 different types of circRNAs and the survival outcomes of lung cancer. Based on our best literature search, our MA included the highest number of prognostic factor studies, and it included primary studies published in 2023. All the studies were conducted in China, and all the participants in the studies are Chinese. Among them, 40 (32 NSCLC + 8 Adenocarcinoma) studies reported on NSCLC, 2 were just lung cancer and only one study reported on SCLC. Regarding the actions of circRNAs on lung cancer, 32 studies reported an association between upregulating circRNAs and lung tumours; and 11 studies reported an association between downregulating circRNAs and lung tumours. In those 32 studies, it was reported that high expression of circRNAs was associated with an unfavorable prognosis by facilitating tumour progression, inducing resistance to immune checkpoint inhibitor therapy, enhancing metastasis etc. 11 studies reported that high expression of circRNAs was associated with a favorable prognosis, as those cirRNAs have downregulating action on cancer cells by inhibiting cancer cell proliferation and enhancing chemosensitivity.

Although we planned to conduct a MA on the association of circRNAs and prognosis in both NSCLC and SCLC, we can only conduct it for NSCLC as only one study reported prognosis for SCLC. This study reported that circRNA cESRP1 expression had downregulating effect in SCLC tissues, playing a crucial role in chemosensitivity by sponging miR-93-5p to inhibit the TGF-β pathway, and it was associated with survival [ 49 ].

The results of our MA were comparable with other published MAs. A MA on the association of expression of downregulating circRNAs and OS in NSCLC showed that high expression of downregulating circRNAs was correlated with favorable OS in both NSCLC and SCLC. Pooled results of those MAs indicated that the expression of upregulating circRNAs was significantly associated with the worse prognosis in NSCLC [ 67 , 68 ]. A MA on the diagnostic and prognostic value of circRNAs in lung cancer also reported a significant association between circRNAs expression and diagnostic and prognostic values in lung cancer patients [ 69 ]. Many types of circRNAs are also correlated with tumour size, lymph node metastasis, distant metastasis, TNM staging, and differentiation, by promoting lung cancer invasion and migration [ 11 ]. Most of the prognostic role of circRNAs was based on the mechanism of microRNA (miRNA) molecular sponge by adsorbing miRNA, regulating the transcription of parental genes, interacting with RNA-binding proteins to play biological roles, and translating proteins [ 70 , 71 , 72 ].

In our MA, three studies reported on ciRS-7 and they reported that high expression of ciRS-7 was associated with a poor prognosis of NSCLC [ 34 , 39 , 41 ]. CiRS-7 was described as associated not only with the poor prognosis of NSCLC, but also with the poor prognosis of other malignancies such as hepatocellular carcinoma and renal cell carcinoma [ 73 , 74 ]. Previously, ciRS-7 was reported to act as a tumour promoter by regulating the miR-139-3p/TAGLN axis and activating the PI3K/AKT signaling pathway to promote tumour progression and metastasis [ 74 ]. A study on lung adenocarcinoma reported that high expression of this circRNA was associated with TNM staging and lymphatic metastasis [ 75 ].

In our MA, circ-100,395, circ-0065214, cESRP1, circ-ITCH, circ-0001649, circ-11,780, circSMARCA5, circCRIM1, circ-0046264, circ-0006427 and circ-0072309 had downregulating effect in NSCLC by playing an important role in NSCLC cell proliferation, cell migration, and apoptosis. Regarding the downregulating action of circRNAs in lung cancer, those circRNAs inhibit the growth and invasion of lung cancer cells for example through the miR-558/TNFAIP1 and TPM1 pathways [ 76 ]. Considering the effect of individual circRNAs, cESRP1 circRNA acted on the chemoresistant cells and augmented chemosensitivity by sponging miR-93-5p in SCLC to inhibit the TGF-β pathway [ 49 ]. Circ-0065214 (circSCAP) directly binds to the SF3A3 protein, facilitating the reduction of SF3A3 by promoting its ubiquitin–proteasome-mediated degradation, which enhances the expression of MDM4-S to finally activate its downstream p53 signaling [ 48 ]. Circ_100395 inhibits the malignancy of NSCLC by targeting miR-141-3p and upregulating LATS2; these can in turn increase phosphorylation of YAP and inactivate the Hippo/YAP pathway [ 47 ]. Moreover, it significantly decreases the tumour volume and weight in vivo [ 77 ]. These downregulating actions of enhancing chemosensitivity and inhibiting tumour invasion can be considered in the management of lung cancer. Accumulated evidence to date highlights the multifaceted role of circRNAs in cancer, especially their regulatory functions across various signaling pathways underscore their potential as biomarkers and therapeutic targets in the field of oncology [ 59 ]. Therefore, regulating the expression level of circRNAs is of great significance to the malignant biological behavior of lung cancer [ 63 ].

There were a few limitations in conducting this MA. Although we aimed to conduct MA on both NSCLC and SCLC, this MA was mainly on NSCLC as only one study on SCLC was included. Although we planned to conduct subgroup analysis on different types of circRNAs, all 43 included studies reported different diverse types of circRNAs and it was not possible to perform subgroup analysis. Subgroup analysis on histopathological types was not able to perform, as most of the studies reported on NSCLC or lung cancer. Subgroup analysis on prognostic association in different treatment regimens was also not performed, as most of the included studies did not report the types of treatment. Another limitation was that all 43 included studies are from China with a Chinese population. If primary studies from other parts of the world could be included, it would be an epidemiologically more informative report.

Our MA confirmed that circRNAs serve as important biomarkers for the prognostic value of lung cancer, especially NSCLC. The findings supported that high expression of upregulating circRNAs is associated with poor OS and poor prognosis; on the other hand, downregulating action of circRNAs are associated with favorable OS and better prognosis. CircRNAs act as tumour-promoting or tumour-suppressing factors to regulate the biological behaviours of lung cancer, such as proliferation, metastasis, and apoptosis, regulate the sensitivity of chemotherapy or targeted drugs and the efficacy of immunotherapy, and provide a preliminary theoretical basis for adjuvant clinical treatment. Moreover, circRNA can be considered a promising novel biomarker for the prognosis of lung cancer, especially NSCLC. The downregulatory action of circRNAs should be considered a promising treatment in the management of lung cancer, especially NSCLC. More translational research should be explored to understand the downregulatory action of circRNAs to be used as a promising treatment in the management of lung cancer.

Data availability

Data are available in a public, open access repository. All data relevant to the study are included in the article or uploaded as supplementary information. The data used to support the findings of this study are included within the manuscript and supplementary files.

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Acknowledgements

The authors are grateful to the participants and researchers of the primary studies in this meta-analysis; and to the IMU University (Formerly known as International Medical University), Malaysia for allowing us to perform this study [ID: BMS I/2022 (04)].

This research work was supported by a Grant from the IMU University, Kuala Lumpur, Malaysia (Project ID: BMS I/2022(04).

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BMed Science, School of Medicine, IMU University, 126, Jalan Jalil Perkasa 19, Bukit Jalil, Kuala Lumpur, 57000, Malaysia

Sanabil Ahsan

Warwick Medical School, The University of Warwick, Coventry, CV4 7AL, UK

Department of Pathology and Pharmacology, School of Medicine, IMU University, 126, Jalan Jalil Perkasa 19, Bukit Jalil, Kuala Lumpur, 57000, Malaysia

Thin Thin Win & Saint Nway Aye

Department of Community Medicine, Faculty of Medicine, Manipal University College Malaysia, Melaka, Malaysia

Nan Nitra Than

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Research design: TTW, SNA; Data collection and extraction: TTW, SA, SNA; Statistical analysis: TTW, SA; Drafting manuscript: SA, TTW, SNA, NNT; Final approval of manuscript: SA, TTW, SNA, NNT.

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Ahsan, S., Win, T.T., Aye, S.N. et al. The role of circular RNAs (circRNAs) as a prognostic factor in lung cancer: a meta-analysis. BMC Cancer 24 , 988 (2024). https://doi.org/10.1186/s12885-024-12704-w

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DOI : https://doi.org/10.1186/s12885-024-12704-w

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Physical therapy students’ experiences of inappropriate patient sexual behavior: a narrative review

Article sidebar, main article content.

Primary objective :  The purpose of this study is to identify the extent to which inappropriate patient sexual behavior (IPSB) is directed toward student physical therapists (PTs) and how this phenomenon is described in the current literature.

Review type :  Narrative review.

Summary of review method :  A search of PubMed, CINAHL Plus, and Academic Search Complete was conducted using the Boolean phrase (‘sexual harassment’ OR ‘sexual assault’ OR ‘inappropriate sexual behavior’ OR ‘sexual behavior’) AND (‘physical therapy’ OR physiotherapy OR ‘physical therapist’ OR physiotherapist). After relevant articles were identified, references were searched for additional relevant material. Data and common themes were identified, extracted, and summarized.

Primary results :  Studies indicate that 84% to 92.9% of PTs have IPSBs directed at them during their careers. There is less information on the rate at which student PTs are targets of IPSB, but the available studies indicate 66.2% to 78% of them experience IPSB during their clinical experiences. In one study, over 22% of PT students experienced severe forms of IPSB during clinical experiences. Other studies show that student PTs and novice PTs respond to IPSB with techniques that are less effective than those used by experienced PTs. Qualitative reports indicate that student PTs feel that they and their clinical instructors are unprepared for IPSB and believe more training on the topic is necessary.

Conclusion :  The available literature indicates that most PT students have IPSB directed at them during their clinical experiences. Students report feeling unprepared and desire more training on this topic. Additional training may reduce IPSB.

Article Details

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License .