zimbardo prison experiment 1973

Stanford Prison Experiment: Zimbardo’s Famous Study

Saul McLeod, PhD

Editor-in-Chief for Simply Psychology

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul McLeod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

Learn about our Editorial Process

Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

On This Page:

• The experiment was conducted in 1971 by psychologist Philip Zimbardo to examine situational forces versus dispositions in human behavior.
• 24 young, healthy, psychologically normal men were randomly assigned to be “prisoners” or “guards” in a simulated prison environment.
• The experiment had to be terminated after only 6 days due to the extreme, pathological behavior emerging in both groups. The situational forces overwhelmed the dispositions of the participants.
• Pacifist young men assigned as guards began behaving sadistically, inflicting humiliation and suffering on the prisoners. Prisoners became blindly obedient and allowed themselves to be dehumanized.
• The principal investigator, Zimbardo, was also transformed into a rigid authority figure as the Prison Superintendent.
• The experiment demonstrated the power of situations to alter human behavior dramatically. Even good, normal people can do evil things when situational forces push them in that direction.

Zimbardo and his colleagues (1973) were interested in finding out whether the brutality reported among guards in American prisons was due to the sadistic personalities of the guards (i.e., dispositional) or had more to do with the prison environment (i.e., situational).

For example, prisoners and guards may have personalities that make conflict inevitable, with prisoners lacking respect for law and order and guards being domineering and aggressive.

Alternatively, prisoners and guards may behave in a hostile manner due to the rigid power structure of the social environment in prisons.

Zimbardo predicted the situation made people act the way they do rather than their disposition (personality).

To study people’s roles in prison situations, Zimbardo converted a basement of the Stanford University psychology building into a mock prison.

He advertised asking for volunteers to participate in a study of the psychological effects of prison life.

The 75 applicants who answered the ad were given diagnostic interviews and personality tests to eliminate candidates with psychological problems, medical disabilities, or a history of crime or drug abuse.

24 men judged to be the most physically & mentally stable, the most mature, & the least involved in antisocial behaviors were chosen to participate.

The participants did not know each other prior to the study and were paid $15 per day to take part in the experiment.

Participants were randomly assigned to either the role of prisoner or guard in a simulated prison environment. There were two reserves, and one dropped out, finally leaving ten prisoners and 11 guards.

Prisoners were treated like every other criminal, being arrested at their own homes, without warning, and taken to the local police station. They were fingerprinted, photographed and ‘booked.’

Then they were blindfolded and driven to the psychology department of Stanford University, where Zimbardo had had the basement set out as a prison, with barred doors and windows, bare walls and small cells. Here the deindividuation process began.

When the prisoners arrived at the prison they were stripped naked, deloused, had all their personal possessions removed and locked away, and were given prison clothes and bedding. They were issued a uniform, and referred to by their number only.

The use of ID numbers was a way to make prisoners feel anonymous. Each prisoner had to be called only by his ID number and could only refer to himself and the other prisoners by number.

Their clothes comprised a smock with their number written on it, but no underclothes. They also had a tight nylon cap to cover their hair, and a locked chain around one ankle.

All guards were dressed in identical uniforms of khaki, and they carried a whistle around their neck and a billy club borrowed from the police. Guards also wore special sunglasses, to make eye contact with prisoners impossible.

Three guards worked shifts of eight hours each (the other guards remained on call). Guards were instructed to do whatever they thought was necessary to maintain law and order in the prison and to command the respect of the prisoners. No physical violence was permitted.

Zimbardo observed the behavior of the prisoners and guards (as a researcher), and also acted as a prison warden.

Within a very short time both guards and prisoners were settling into their new roles, with the guards adopting theirs quickly and easily.

Asserting Authority

Within hours of beginning the experiment, some guards began to harass prisoners. At 2:30 A.M. prisoners were awakened from sleep by blasting whistles for the first of many “counts.”

The counts served as a way to familiarize the prisoners with their numbers. More importantly, they provided a regular occasion for the guards to exercise control over the prisoners.

The prisoners soon adopted prisoner-like behavior too. They talked about prison issues a great deal of the time. They ‘told tales’ on each other to the guards.

They started taking the prison rules very seriously, as though they were there for the prisoners’ benefit and infringement would spell disaster for all of them. Some even began siding with the guards against prisoners who did not obey the rules.

Physical Punishment

The prisoners were taunted with insults and petty orders, they were given pointless and boring tasks to accomplish, and they were generally dehumanized.

Push-ups were a common form of physical punishment imposed by the guards. One of the guards stepped on the prisoners” backs while they did push-ups, or made other prisoners sit on the backs of fellow prisoners doing their push-ups.

Asserting Independence

Because the first day passed without incident, the guards were surprised and totally unprepared for the rebellion which broke out on the morning of the second day.

During the second day of the experiment, the prisoners removed their stocking caps, ripped off their numbers, and barricaded themselves inside the cells by putting their beds against the door.

The guards called in reinforcements. The three guards who were waiting on stand-by duty came in and the night shift guards voluntarily remained on duty.

Putting Down the Rebellion

The guards retaliated by using a fire extinguisher which shot a stream of skin-chilling carbon dioxide, and they forced the prisoners away from the doors. Next, the guards broke into each cell, stripped the prisoners naked and took the beds out.

The ringleaders of the prisoner rebellion were placed into solitary confinement. After this, the guards generally began to harass and intimidate the prisoners.

Special Privileges

One of the three cells was designated as a “privilege cell.” The three prisoners least involved in the rebellion were given special privileges. The guards gave them back their uniforms and beds and allowed them to wash their hair and brush their teeth.

Privileged prisoners also got to eat special food in the presence of the other prisoners who had temporarily lost the privilege of eating. The effect was to break the solidarity among prisoners.

Consequences of the Rebellion

Over the next few days, the relationships between the guards and the prisoners changed, with a change in one leading to a change in the other. Remember that the guards were firmly in control and the prisoners were totally dependent on them.

As the prisoners became more dependent, the guards became more derisive towards them. They held the prisoners in contempt and let the prisoners know it. As the guards’ contempt for them grew, the prisoners became more submissive.

As the prisoners became more submissive, the guards became more aggressive and assertive. They demanded ever greater obedience from the prisoners. The prisoners were dependent on the guards for everything, so tried to find ways to please the guards, such as telling tales on fellow prisoners.

Prisoner #8612

Less than 36 hours into the experiment, Prisoner #8612 began suffering from acute emotional disturbance, disorganized thinking, uncontrollable crying, and rage.

After a meeting with the guards where they told him he was weak, but offered him “informant” status, #8612 returned to the other prisoners and said “You can”t leave. You can’t quit.”

Soon #8612 “began to act ‘crazy,’ to scream, to curse, to go into a rage that seemed out of control.” It wasn’t until this point that the psychologists realized they had to let him out.

A Visit from Parents

The next day, the guards held a visiting hour for parents and friends. They were worried that when the parents saw the state of the jail, they might insist on taking their sons home. Guards washed the prisoners, had them clean and polish their cells, fed them a big dinner and played music on the intercom.

After the visit, rumors spread of a mass escape plan. Afraid that they would lose the prisoners, the guards and experimenters tried to enlist help and facilities of the Palo Alto police department.

The guards again escalated the level of harassment, forcing them to do menial, repetitive work such as cleaning toilets with their bare hands.

Catholic Priest

Zimbardo invited a Catholic priest who had been a prison chaplain to evaluate how realistic our prison situation was. Half of the prisoners introduced themselves by their number rather than name.

The chaplain interviewed each prisoner individually. The priest told them the only way they would get out was with the help of a lawyer.

Prisoner #819

Eventually, while talking to the priest, #819 broke down and began to cry hysterically, just like two previously released prisoners had.

The psychologists removed the chain from his foot, the cap off his head, and told him to go and rest in a room that was adjacent to the prison yard. They told him they would get him some food and then take him to see a doctor.

While this was going on, one of the guards lined up the other prisoners and had them chant aloud:

“Prisoner #819 is a bad prisoner. Because of what Prisoner #819 did, my cell is a mess, Mr. Correctional Officer.”

The psychologists realized #819 could hear the chanting and went back into the room where they found him sobbing uncontrollably. The psychologists tried to get him to agree to leave the experiment, but he said he could not leave because the others had labeled him a bad prisoner.

Back to Reality

At that point, Zimbardo said, “Listen, you are not #819. You are [his name], and my name is Dr. Zimbardo. I am a psychologist, not a prison superintendent, and this is not a real prison. This is just an experiment, and those are students, not prisoners, just like you. Let’s go.”

He stopped crying suddenly, looked up and replied, “Okay, let’s go,“ as if nothing had been wrong.

An End to the Experiment

Zimbardo (1973) had intended that the experiment should run for two weeks, but on the sixth day, it was terminated, due to the emotional breakdowns of prisoners, and excessive aggression of the guards.

Christina Maslach, a recent Stanford Ph.D. brought in to conduct interviews with the guards and prisoners, strongly objected when she saw the prisoners being abused by the guards.

Filled with outrage, she said, “It’s terrible what you are doing to these boys!” Out of 50 or more outsiders who had seen our prison, she was the only one who ever questioned its morality.

Zimbardo (2008) later noted, “It wasn’t until much later that I realized how far into my prison role I was at that point — that I was thinking like a prison superintendent rather than a research psychologist.“

This led him to prioritize maintaining the experiment’s structure over the well-being and ethics involved, thereby highlighting the blurring of roles and the profound impact of the situation on human behavior.

Here’s a quote that illustrates how Philip Zimbardo, initially the principal investigator, became deeply immersed in his role as the “Stanford Prison Superintendent (April 19, 2011):

“By the third day, when the second prisoner broke down, I had already slipped into or been transformed into the role of “Stanford Prison Superintendent.” And in that role, I was no longer the principal investigator, worried about ethics. When a prisoner broke down, what was my job? It was to replace him with somebody on our standby list. And that’s what I did. There was a weakness in the study in not separating those two roles. I should only have been the principal investigator, in charge of two graduate students and one undergraduate.”

According to Zimbardo and his colleagues, the Stanford Prison Experiment revealed how people will readily conform to the social roles they are expected to play, especially if the roles are as strongly stereotyped as those of the prison guards.

Because the guards were placed in a position of authority, they began to act in ways they would not usually behave in their normal lives.

The “prison” environment was an important factor in creating the guards’ brutal behavior (none of the participants who acted as guards showed sadistic tendencies before the study).

Therefore, the findings support the situational explanation of behavior rather than the dispositional one.

Zimbardo proposed that two processes can explain the prisoner’s “final submission.”

Deindividuation may explain the behavior of the participants; especially the guards. This is a state when you become so immersed in the norms of the group that you lose your sense of identity and personal responsibility.

The guards may have been so sadistic because they did not feel what happened was down to them personally – it was a group norm. They also may have lost their sense of personal identity because of the uniform they wore.

Also, learned helplessness could explain the prisoner’s submission to the guards. The prisoners learned that whatever they did had little effect on what happened to them. In the mock prison the unpredictable decisions of the guards led the prisoners to give up responding.

After the prison experiment was terminated, Zimbardo interviewed the participants. Here’s an excerpt:

‘Most of the participants said they had felt involved and committed. The research had felt “real” to them. One guard said, “I was surprised at myself. I made them call each other names and clean the toilets out with their bare hands. I practically considered the prisoners cattle and I kept thinking I had to watch out for them in case they tried something.” Another guard said “Acting authoritatively can be fun. Power can be a great pleasure.” And another: “… during the inspection I went to Cell Two to mess up a bed which a prisoner had just made and he grabbed me, screaming that he had just made it and that he was not going to let me mess it up. He grabbed me by the throat and although he was laughing I was pretty scared. I lashed out with my stick and hit him on the chin although not very hard, and when I freed myself I became angry.”’

Most of the guards found it difficult to believe that they had behaved in the brutal ways that they had. Many said they hadn’t known this side of them existed or that they were capable of such things.

The prisoners, too, couldn’t believe that they had responded in the submissive, cowering, dependent way they had. Several claimed to be assertive types normally.

When asked about the guards, they described the usual three stereotypes that can be found in any prison: some guards were good, some were tough but fair, and some were cruel.

A further explanation for the behavior of the participants can be described in terms of reinforcement.  The escalation of aggression and abuse by the guards could be seen as being due to the positive reinforcement they received both from fellow guards and intrinsically in terms of how good it made them feel to have so much power.

Similarly, the prisoners could have learned through negative reinforcement that if they kept their heads down and did as they were told, they could avoid further unpleasant experiences.

Critical Evaluation

Ecological validity.

The Stanford Prison Experiment is criticized for lacking ecological validity in its attempt to simulate a real prison environment. Specifically, the “prison” was merely a setup in the basement of Stanford University’s psychology department.

The student “guards” lacked professional training, and the experiment’s duration was much shorter than real prison sentences. Furthermore, the participants, who were college students, didn’t reflect the diverse backgrounds typically found in actual prisons in terms of ethnicity, education, and socioeconomic status.

None had prior prison experience, and they were chosen due to their mental stability and low antisocial tendencies. Additionally, the mock prison lacked spaces for exercise or rehabilitative activities.

Demand characteristics

Demand characteristics could explain the findings of the study. Most of the guards later claimed they were simply acting. Because the guards and prisoners were playing a role, their behavior may not be influenced by the same factors which affect behavior in real life. This means the study’s findings cannot be reasonably generalized to real life, such as prison settings. I.e, the study has low ecological validity.

One of the biggest criticisms is that strong demand characteristics confounded the study. Banuazizi and Movahedi (1975) found that the majority of respondents, when given a description of the study, were able to guess the hypothesis and predict how participants were expected to behave.

This suggests participants may have simply been playing out expected roles rather than genuinely conforming to their assigned identities.

In addition, revelations by Zimbardo (2007) indicate he actively encouraged the guards to be cruel and oppressive in his orientation instructions prior to the start of the study. For example, telling them “they [the prisoners] will be able to do nothing and say nothing that we don’t permit.”

He also tacitly approved of abusive behaviors as the study progressed. This deliberate cueing of how participants should act, rather than allowing behavior to unfold naturally, indicates the study findings were likely a result of strong demand characteristics rather than insightful revelations about human behavior.

However, there is considerable evidence that the participants did react to the situation as though it was real. For example, 90% of the prisoners’ private conversations, which were monitored by the researchers, were on the prison conditions, and only 10% of the time were their conversations about life outside of the prison.

The guards, too, rarely exchanged personal information during their relaxation breaks – they either talked about ‘problem prisoners,’ other prison topics, or did not talk at all. The guards were always on time and even worked overtime for no extra pay.

When the prisoners were introduced to a priest, they referred to themselves by their prison number, rather than their first name. Some even asked him to get a lawyer to help get them out.

Fourteen years after his experience as prisoner 8612 in the Stanford Prison Experiment, Douglas Korpi, now a prison psychologist, reflected on his time and stated (Musen and Zimbardo 1992):

“The Stanford Prison Experiment was a very benign prison situation and it promotes everything a normal prison promotes — the guard role promotes sadism, the prisoner role promotes confusion and shame”.

Sample bias

The study may also lack population validity as the sample comprised US male students. The study’s findings cannot be applied to female prisons or those from other countries. For example, America is an individualist culture (where people are generally less conforming), and the results may be different in collectivist cultures (such as Asian countries).

Carnahan and McFarland (2007) have questioned whether self-selection may have influenced the results – i.e., did certain personality traits or dispositions lead some individuals to volunteer for a study of “prison life” in the first place?

All participants completed personality measures assessing: aggression, authoritarianism, Machiavellianism, narcissism, social dominance, empathy, and altruism. Participants also answered questions on mental health and criminal history to screen out any issues as per the original SPE.

Results showed that volunteers for the prison study, compared to the control group, scored significantly higher on aggressiveness, authoritarianism, Machiavellianism, narcissism, and social dominance. They scored significantly lower on empathy and altruism.

A follow-up role-playing study found that self-presentation biases could not explain these differences. Overall, the findings suggest that volunteering for the prison study was influenced by personality traits associated with abusive tendencies.

Zimbardo’s conclusion may be wrong

While implications for the original SPE are speculative, this lends support to a person-situation interactionist perspective, rather than a purely situational account.

It implies that certain individuals are drawn to and selected into situations that fit their personality, and that group composition can shape behavior through mutual reinforcement.

Contributions to psychology

Another strength of the study is that the harmful treatment of participants led to the formal recognition of ethical  guidelines by the American Psychological Association. Studies must now undergo an extensive review by an institutional review board (US) or ethics committee (UK) before they are implemented.

Most institutions, such as universities, hospitals, and government agencies, require a review of research plans by a panel. These boards review whether the potential benefits of the research are justifiable in light of the possible risk of physical or psychological harm.

These boards may request researchers make changes to the study’s design or procedure, or, in extreme cases, deny approval of the study altogether.

Contribution to prison policy

A strength of the study is that it has altered the way US prisons are run. For example, juveniles accused of federal crimes are no longer housed before trial with adult prisoners (due to the risk of violence against them).

However, in the 25 years since the SPE, U.S. prison policy has transformed in ways counter to SPE insights (Haney & Zimbardo, 1995):

• Rehabilitation was abandoned in favor of punishment and containment. Prison is now seen as inflicting pain rather than enabling productive re-entry.
• Sentencing became rigid rather than accounting for inmates’ individual contexts. Mandatory minimums and “three strikes” laws over-incarcerate nonviolent crimes.
• Prison construction boomed, and populations soared, disproportionately affecting minorities. From 1925 to 1975, incarceration rates held steady at around 100 per 100,000. By 1995, rates tripled to over 600 per 100,000.
• Drug offenses account for an increasing proportion of prisoners. Nonviolent drug offenses make up a large share of the increased incarceration.
• Psychological perspectives have been ignored in policymaking. Legislators overlooked insights from social psychology on the power of contexts in shaping behavior.
• Oversight retreated, with courts deferring to prison officials and ending meaningful scrutiny of conditions. Standards like “evolving decency” gave way to “legitimate” pain.
• Supermax prisons proliferated, isolating prisoners in psychological trauma-inducing conditions.

The authors argue psychologists should reengage to:

• Limit the use of imprisonment and adopt humane alternatives based on the harmful effects of prison environments
• Assess prisons’ total environments, not just individual conditions, given situational forces interact
• Prepare inmates for release by transforming criminogenic post-release contexts
• Address socioeconomic risk factors, not just incarcerate individuals
• Develop contextual prediction models vs. focusing only on static traits
• Scrutinize prison systems independently, not just defer to officials shaped by those environments
• Generate creative, evidence-based reforms to counter over-punitive policies

Psychology once contributed to a more humane system and can again counter the U.S. “rage to punish” with contextual insights (Haney & Zimbardo, 1998).

Evidence for situational factors

Zimbardo (1995) further demonstrates the power of situations to elicit evil actions from ordinary, educated people who likely would never have done such things otherwise. It was another situation-induced “transformation of human character.”

• Unit 731 was a covert biological and chemical warfare research unit of the Japanese army during WWII.
• It was led by General Shiro Ishii and involved thousands of doctors and researchers.
• Unit 731 set up facilities near Harbin, China to conduct lethal human experimentation on prisoners, including Allied POWs.
• Experiments involved exposing prisoners to things like plague, anthrax, mustard gas, and bullets to test biological weapons. They infected prisoners with diseases and monitored their deaths.
• At least 3,000 prisoners died from these brutal experiments. Many were killed and dissected.
• The doctors in Unit 731 obeyed orders unquestioningly and conducted these experiments in the name of “medical science.”
• After the war, the vast majority of doctors who participated faced no punishment and went on to have prestigious careers. This was largely covered up by the U.S. in exchange for data.
• It shows how normal, intelligent professionals can be led by situational forces to systematically dehumanize victims and conduct incredibly cruel and lethal experiments on people.
• Even healers trained to preserve life used their expertise to destroy lives when the situational forces compelled obedience, nationalism, and wartime enmity.

Evidence for an interactionist approach

The results are also relevant for explaining abuses by American guards at Abu Ghraib prison in Iraq.

An interactionist perspective recognizes that volunteering for roles as prison guards attracts those already prone to abusive tendencies, which are intensified by the prison context.

This counters a solely situationist view of good people succumbing to evil situational forces.

Ethical Issues

The study has received many ethical criticisms, including lack of fully informed consent by participants as Zimbardo himself did not know what would happen in the experiment (it was unpredictable). Also, the prisoners did not consent to being “arrested” at home. The prisoners were not told partly because final approval from the police wasn’t given until minutes before the participants decided to participate, and partly because the researchers wanted the arrests to come as a surprise. However, this was a breach of the ethics of Zimbardo’s own contract that all of the participants had signed.

Protection of Participants

Participants playing the role of prisoners were not protected from psychological harm, experiencing incidents of humiliation and distress. For example, one prisoner had to be released after 36 hours because of uncontrollable bursts of screaming, crying, and anger.

Here’s a quote from Philip G. Zimbardo, taken from an interview on the Stanford Prison Experiment’s 40th anniversary (April 19, 2011):

“In the Stanford prison study, people were stressed, day and night, for 5 days, 24 hours a day. There’s no question that it was a high level of stress because five of the boys had emotional breakdowns, the first within 36 hours. Other boys that didn’t have emotional breakdowns were blindly obedient to corrupt authority by the guards and did terrible things to each other. And so it is no question that that was unethical. You can’t do research where you allow people to suffer at that level.”

“After the first one broke down, we didn’t believe it. We thought he was faking. There was actually a rumor he was faking to get out. He was going to bring his friends in to liberate the prison. And/or we believed our screening procedure was inadequate, [we believed] that he had some mental defect that we did not pick up. At that point, by the third day, when the second prisoner broke down, I had already slipped into or been transformed into the role of “Stanford Prison Superintendent.” And in that role, I was no longer the principal investigator, worried about ethics.”

However, in Zimbardo’s defense, the emotional distress experienced by the prisoners could not have been predicted from the outset.

Approval for the study was given by the Office of Naval Research, the Psychology Department, and the University Committee of Human Experimentation.

This Committee also did not anticipate the prisoners’ extreme reactions that were to follow. Alternative methodologies were looked at that would cause less distress to the participants but at the same time give the desired information, but nothing suitable could be found.

Withdrawal 

Although guards were explicitly instructed not to physically harm prisoners at the beginning of the Stanford Prison Experiment, they were allowed to induce feelings of boredom, frustration, arbitrariness, and powerlessness among the inmates.

This created a pervasive atmosphere where prisoners genuinely believed and even reinforced among each other, that they couldn’t leave the experiment until their “sentence” was completed, mirroring the inescapability of a real prison.

Even though two participants (8612 and 819) were released early, the impact of the environment was so profound that prisoner 416, reflecting on the experience two months later, described it as a “prison run by psychologists rather than by the state.”

Extensive group and individual debriefing sessions were held, and all participants returned post-experimental questionnaires several weeks, then several months later, and then at yearly intervals. Zimbardo concluded there were no lasting negative effects.

Zimbardo also strongly argues that the benefits gained from our understanding of human behavior and how we can improve society should outbalance the distress caused by the study.

However, it has been suggested that the US Navy was not so much interested in making prisons more human and were, in fact, more interested in using the study to train people in the armed services to cope with the stresses of captivity.

Discussion Questions

What are the effects of living in an environment with no clocks, no view of the outside world, and minimal sensory stimulation?

Consider the psychological consequences of stripping, delousing, and shaving the heads of prisoners or members of the military. Whattransformations take place when people go through an experience like this?

The prisoners could have left at any time, and yet, they didn’t. Why?

After the study, how do you think the prisoners and guards felt?

If you were the experimenter in charge, would you have done this study? Would you have terminated it earlier? Would you have conducted a follow-up study?

Frequently Asked Questions

What happened to prisoner 8612 after the experiment.

Douglas Korpi, as prisoner 8612, was the first to show signs of severe distress and demanded to be released from the experiment. He was released on the second day, and his reaction to the simulated prison environment highlighted the study’s ethical issues and the potential harm inflicted on participants.

After the experiment, Douglas Korpi graduated from Stanford University and earned a Ph.D. in clinical psychology. He pursued a career as a psychotherapist, helping others with their mental health struggles.

Why did Zimbardo not stop the experiment?

Zimbardo did not initially stop the experiment because he became too immersed in his dual role as the principal investigator and the prison superintendent, causing him to overlook the escalating abuse and distress among participants.

It was only after an external observer, Christina Maslach, raised concerns about the participants’ well-being that Zimbardo terminated the study.

What happened to the guards in the Stanford Prison Experiment?

In the Stanford Prison Experiment, the guards exhibited abusive and authoritarian behavior, using psychological manipulation, humiliation, and control tactics to assert dominance over the prisoners. This ultimately led to the study’s early termination due to ethical concerns.

What did Zimbardo want to find out?

Zimbardo aimed to investigate the impact of situational factors and power dynamics on human behavior, specifically how individuals would conform to the roles of prisoners and guards in a simulated prison environment.

He wanted to explore whether the behavior displayed in prisons was due to the inherent personalities of prisoners and guards or the result of the social structure and environment of the prison itself.

What were the results of the Stanford Prison Experiment?

The results of the Stanford Prison Experiment showed that situational factors and power dynamics played a significant role in shaping participants’ behavior. The guards became abusive and authoritarian, while the prisoners became submissive and emotionally distressed.

The experiment revealed how quickly ordinary individuals could adopt and internalize harmful behaviors due to their assigned roles and the environment.

Banuazizi, A., & Movahedi, S. (1975). Interpersonal dynamics in a simulated prison: A methodological analysis. American Psychologist, 30 , 152-160.

Carnahan, T., & McFarland, S. (2007). Revisiting the Stanford prison experiment: Could participant self-selection have led to the cruelty? Personality and Social Psychology Bulletin, 33, 603-614.

Drury, S., Hutchens, S. A., Shuttlesworth, D. E., & White, C. L. (2012). Philip G. Zimbardo on his career and the Stanford Prison Experiment’s 40th anniversary.  History of Psychology ,  15 (2), 161.

Griggs, R. A., & Whitehead, G. I., III. (2014). Coverage of the Stanford Prison Experiment in introductory social psychology textbooks. Teaching of Psychology, 41 , 318 –324.

Haney, C., Banks, W. C., & Zimbardo, P. G. (1973). A study of prisoners and guards in a simulated prison . Naval Research Review , 30, 4-17.

Haney, C., & Zimbardo, P. (1998). The past and future of U.S. prison policy: Twenty-five years after the Stanford Prison Experiment.  American Psychologist, 53 (7), 709–727.

Musen, K. & Zimbardo, P. (1992) (DVD) Quiet Rage: The Stanford Prison Experiment Documentary.

Zimbardo, P. G. (Consultant, On-Screen Performer), Goldstein, L. (Producer), & Utley, G. (Correspondent). (1971, November 26). Prisoner 819 did a bad thing: The Stanford Prison Experiment [Television series episode]. In L. Goldstein (Producer), Chronolog. New York, NY: NBC-TV.

Zimbardo, P. G. (1973). On the ethics of intervention in human psychological research: With special reference to the Stanford prison experiment.  Cognition ,  2 (2), 243-256.

Zimbardo, P. G. (1995). The psychology of evil: A situationist perspective on recruiting good people to engage in anti-social acts.  Japanese Journal of Social Psychology ,  11 (2), 125-133.

Zimbardo, P.G. (2007). The Lucifer effect: Understanding how good people turn evil . New York, NY: Random House.

Further Information

• Reicher, S., & Haslam, S. A. (2006). Rethinking the psychology of tyranny: The BBC prison study. The British Journal of Social Psychology, 45 , 1.
• Coverage of the Stanford Prison Experiment in introductory psychology textbooks
• The Stanford Prison Experiment Official Website

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The Stanford Prison Experiment

• Participants
• Setting and Procedure

In August of 1971, psychologist Philip Zimbardo and his colleagues created an experiment to determine the impacts of being a prisoner or prison guard. The Stanford Prison Experiment, also known as the Zimbardo Prison Experiment, went on to become one of the best-known studies in psychology's history —and one of the most controversial.

This study has long been a staple in textbooks, articles, psychology classes, and even movies. Learn what it entailed, what was learned, and the criticisms that have called the experiment's scientific merits and value into question.

Purpose of the Stanford Prison Experiment

Zimbardo was a former classmate of the psychologist Stanley Milgram . Milgram is best known for his famous obedience experiment , and Zimbardo was interested in expanding upon Milgram's research. He wanted to further investigate the impact of situational variables on human behavior.

Specifically, the researchers wanted to know how participants would react when placed in a simulated prison environment. They wondered if physically and psychologically healthy people who knew they were participating in an experiment would change their behavior in a prison-like setting.

Participants in the Stanford Prison Experiment

To carry out the experiment, researchers set up a mock prison in the basement of Stanford University's psychology building. They then selected 24 undergraduate students to play the roles of both prisoners and guards.

Participants were chosen from a larger group of 70 volunteers based on having no criminal background, no psychological issues , and no significant medical conditions. Each volunteer agreed to participate in the Stanford Prison Experiment for one to two weeks in exchange for $15 a day.

Setting and Procedures

The simulated prison included three six-by-nine-foot prison cells. Each cell held three prisoners and included three cots. Other rooms across from the cells were utilized for the jail guards and warden. One tiny space was designated as the solitary confinement room, and yet another small room served as the prison yard.

The 24 volunteers were randomly assigned to either the prisoner or guard group. Prisoners were to remain in the mock prison 24 hours a day during the study. Guards were assigned to work in three-man teams for eight-hour shifts. After each shift, they were allowed to return to their homes until their next shift.

Researchers were able to observe the behavior of the prisoners and guards using hidden cameras and microphones.

Results of the Stanford Prison Experiment

So what happened in the Zimbardo experiment? While originally slated to last 14 days, it had to be stopped after just six due to what was happening to the student participants. The guards became abusive and the prisoners began to show signs of extreme stress and anxiety .

It was noted that:

• While the prisoners and guards were allowed to interact in any way they wanted, the interactions were hostile or even dehumanizing.
• The guards began to become aggressive and abusive toward the prisoners while the prisoners became passive and depressed.
• Five of the prisoners began to experience severe negative emotions , including crying and acute anxiety, and had to be released from the study early.

Even the researchers themselves began to lose sight of the reality of the situation. Zimbardo, who acted as the prison warden, overlooked the abusive behavior of the jail guards until graduate student Christina Maslach voiced objections to the conditions in the simulated prison and the morality of continuing the experiment.

One possible explanation for the results of this experiment is the idea of deindividuation , which states that being part of a large group can make us more likely to perform behaviors we would otherwise not do on our own.

Impact of the Zimbardo Prison Experiment

The experiment became famous and was widely cited in textbooks and other publications. According to Zimbardo and his colleagues, the Stanford Prison Experiment demonstrated the powerful role that the situation can play in human behavior.

Because the guards were placed in a position of power, they began to behave in ways they would not usually act in their everyday lives or other situations. The prisoners, placed in a situation where they had no real control , became submissive and depressed.

In 2011, the Stanford Alumni Magazine featured a retrospective of the Stanford Prison Experiment in honor of the experiment’s 40th anniversary. The article contained interviews with several people involved, including Zimbardo and other researchers as well as some of the participants.

In the interviews, Richard Yacco, one of the prisoners in the experiment, suggested that the experiment demonstrated the power that societal roles and expectations can play in a person's behavior.

In 2015, the experiment became the topic of a feature film titled The Stanford Prison Experiment that dramatized the events of the 1971 study.

Criticisms of the Stanford Prison Experiment

In the years since the experiment was conducted, there have been a number of critiques of the study. Some of these include:

Ethical Issues

The Stanford Prison Experiment is frequently cited as an example of unethical research. It could not be replicated by researchers today because it fails to meet the standards established by numerous ethical codes, including the Code of Ethics of the American Psychological Association .

Why was Zimbardo's experiment unethical?

Zimbardo's experiment was unethical due to a lack of fully informed consent, abuse of participants, and lack of appropriate debriefings. More recent findings suggest there were other significant ethical issues that compromise the experiment's scientific standing, including the fact that experimenters may have encouraged abusive behaviors.

Lack of Generalizability

Other critics suggest that the study lacks generalizability due to a variety of factors. The unrepresentative sample of participants (mostly white and middle-class males) makes it difficult to apply the results to a wider population.

Lack of Realism

The Zimbardo Prison Experiment is also criticized for its lack of ecological validity. Ecological validity refers to the degree of realism with which a simulated experimental setup matches the real-world situation it seeks to emulate.

While the researchers did their best to recreate a prison setting, it is simply not possible to perfectly mimic all the environmental and situational variables of prison life. Because there may have been factors related to the setting and situation that influenced how the participants behaved, it may not truly represent what might happen outside of the lab.

Recent Criticisms

More recent examination of the experiment's archives and interviews with participants have revealed major issues with the research method , design, and procedures used. Together, these call the study's validity, value, and even authenticity into question.

These reports, including examinations of the study's records and new interviews with participants, have also cast doubt on some of its key findings and assumptions.

Among the issues described:

• One participant suggested that he faked a breakdown so he could leave the experiment because he was worried about failing his classes.
• Other participants also reported altering their behavior in a way designed to "help" the experiment .
• Evidence suggests that the experimenters encouraged the guards' behavior and played a role in fostering the abusive actions of the guards.

In 2019, the journal American Psychologist published an article debunking the famed experiment. It detailed the study's lack of scientific merit and concluded that the Stanford Prison Experiment was "an incredibly flawed study that should have died an early death."

In a statement posted on the experiment's official website, Zimbardo maintains that these criticisms do not undermine the main conclusion of the study—that situational forces can alter individual actions both in positive and negative ways.

The Stanford Prison Experiment is well known both inside and outside the field of psychology . While the study has long been criticized for many reasons, more recent criticisms of the study's procedures shine a brighter light on the experiment's scientific shortcomings.

Stanford University. About the Stanford Prison Experiment .

Stanford Prison Experiment. 2. Setting up .

Sommers T. An interview with Philip Zimbardo . The Believer.

Ratnesar R. The menace within . Stanford Magazine.

Jabbar A, Muazzam A, Sadaqat S. An unveiling the ethical quandaries: A critical analysis of the Stanford Prison Experiment as a mirror of Pakistani society . J Bus Manage Res . 2024;3(1):629-638.

Horn S. Landmark Stanford Prison Experiment criticized as a sham . Prison Legal News .

Bartels JM. The Stanford Prison Experiment in introductory psychology textbooks: A content analysis .  Psychol Learn Teach . 2015;14(1):36-50. doi:10.1177/1475725714568007

American Psychological Association. Ecological validity .

Blum B. The lifespan of a lie . Medium .

Le Texier T. Debunking the Stanford Prison Experiment . Am Psychol . 2019;74(7):823-839. doi:10.1037/amp0000401

Stanford Prison Experiment. Philip Zimbardo's response to recent criticisms of the Stanford Prison Experiment .

By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

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Conformity to Social Roles as Investigated by Zimbardo

Last updated 22 Mar 2021

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Zimbardo (1973) conducted an extremely controversial study on conformity to social roles, called the Stanford Prison Experiment.

His aim was to examine whether people would conform to the social roles of a prison guard or prisoner, when placed in a mock prison environment. Furthermore, he also wanted to examine whether the behaviour displayed in prisons was due to internal dispositional factors, the people themselves, or external situational factors, the environment and conditions of the prison.

Zimbardo’s sample consisted of 21 male university students who volunteered in response to a newspaper advert. The participants were selected on the basis of their physical and mental stability and were each paid $15 a day to take part. The participants were randomly assigned to one of two social roles, prisoners or guards.

Zimbardo wanted to make the experience as realistic as possible, turning the basement of Stanford University into a mock prison. Furthermore, the ‘prisoners’ were arrested by real local police and fingerprinted, stripped and given a numbered smocked to wear, with chains placed around their ankles. The guards were given uniforms, dark reflective sunglasses, handcuffs and a truncheon. The guards were instructed to run the prison without using physical violence. The experiment was set to run for two weeks.

Zimbardo found that both the prisoners and guards quickly identified with their social roles. Within days the prisoners rebelled, but this was quickly crushed by the guards, who then grew increasingly abusive towards the prisoners. The guards dehumanised the prisoners, waking them during the night and forcing them to clean toilets with their bare hands; the prisoners became increasingly submissive, identifying further with their subordinate role.

Five of the prisoners were released from the experiment early, because of their adverse reactions to the physical and mental torment, for example, crying and extreme anxiety. Although the experiment was set to run for two weeks, it was terminated after just six days, when fellow postgraduate student Christina Maslach convinced Zimbardo that conditions in his experiment were inhumane. [Maslach later became Zimbardo’s wife].

Zimbardo concluded that people quickly conform to social roles, even when the role goes against their moral principles. Furthermore, he concluded that situational factors were largely responsible for the behaviour found, as none of the participants had ever demonstrated these behaviours previously.

Evaluation of Zimbardo

A recent replication of the Stanford Prison Experiment, carried out by Reicher and Haslam (2006), contradicts the findings of Zimbardo.

Reicher and Haslam replicated Zimbardo’s research by randomly assigning 15 men to the role of prisoner or guard. In this replication, the participants did not conform to their social roles automatically. For example, the guards did not identify with their status and refused to impose their authority; the prisoners identified as a group to challenge the guard’s authority, which resulted in a shift of power and a collapse of the prison system. These results clearly contradict the findings of Zimbardo and suggest that conformity to social roles may not automatic, as Zimbardo originally implied.

Furthermore, individual differences and personality also determine the extent to which a person conforms to social roles. In Zimbardo’s original experiment the behaviour of the guards varied dramatically, from extremely sadistic behaviour to a few good guards who helped the prisoners. This suggests that situational factors are not the only cause of conformity to social roles and dispositional factors also play a role.

Zimbardo’s experiment has been heavily criticised for breaking many ethical guidelines, in particular, protection from harm. Five of the prisoners left the experiment early because of their adverse reactions to the physical and mental torment. Furthermore, some of the guards reported feelings of anxiety and guilt, as a result of their actions during the Stanford Prison Experiment. Although Zimbardo followed the ethical guidelines of Stanford University and debriefed his participants afterwards, he acknowledged that the study should have been stopped earlier.

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Demonstrating the Power of Social Situations via a Simulated Prison Experiment

A person-centered analysis of human behavior attributes most behavior change, in positive or negative directions, to internal, dispositional features of individuals. The factors commonly believed to direct behavior are to be found in the operation of genes, temperament, personality traits, personal pathologies and virtues. A situation-centered approach, in contrast, focuses on factors external to the person, to the behavioral context in which individuals are functioning. Although human behavior is almost always a function of the interaction of person and situation, social psychologists have called attention to the attributional biases in much of psychology and among the general public that overestimates the importance of dispositional factors while underestimating situational factors. This "fundamental attribution error" they argue, leads to a misrepresentation of both causal determinants and means for modifying undesirable behavior patterns. Research by social psychologist Stanley Milgram, PhD, (1974; see also Blass, 1999) was one of the earliest demonstrations of the extent to which a large sample of ordinary American citizens could be led to blindly obey unjust authority in delivering extreme levels of shock to an innocent "victim."

The Stanford Prison Experiment extended that analysis to demonstrate the surprisingly profound impact of institutional forces on the behavior of normal, healthy participants. Philip Zimbardo, PhD, and his research team of Craig Haney, Curtis Banks, David Jaffe, and ex convict consultant, Carlo Prescott (Zimbardo, Haney, Banks, & Jaffe, 1973) designed a study that separated the usual dispositional factors among correctional personnel and prisoners from the situational factors that characterize many prisons. They wanted to determine what prison-like settings bring out in people that are not confounded by what people bring into prisons. They sought to discover to what extent the violence and anti-social behaviors often found in prisons can be traced to the "bad apples" that go into prisons or to the "bad barrels" (the prisons themselves) that can corrupt behavior of even ordinary, good people.

The study was conducted this way: College students from all over the United States who answered a city newspaper ad for participants in a study of prison life were personally interviewed, given a battery of personality tests, and completed background surveys that enabled the researchers to pre-select only those who were mentally and physically healthy, normal and well adjusted. They were randomly assigned to role-play either prisoners or guards in the simulated prison setting constructed in the basement of Stanford University's Psychology Department. The prison setting was designed as functional simulation of the central features present in the psychology of imprisonment (Zimbardo, Maslach, & Haney, 1999). Read a full description of the methodology, chronology of daily events and transformations of human character that were revealed.

The major results of the study can be summarized as: many of the normal, healthy mock prisoners suffered such intense emotional stress reactions that they had to be released in a matter of days; most of the other prisoners acted like zombies totally obeying the demeaning orders of the guards; the distress of the prisoners was caused by their sense of powerlessness induced by the guards who began acting in cruel, dehumanizing and even sadistic ways. The study was terminated prematurely because it was getting out of control in the extent of degrading actions being perpetrated by the guards against the prisoners - all of whom had been normal, healthy, ordinary young college students less than a week before.

Significance

Practical application.

The lessons of the Stanford Prison Experiment have gone well beyond the classroom (Haney & Zimbardo, 1998). Zimbardo was invited to give testimony to a Congressional Committee investigating the causes of prison riots (Zimbardo, 1971), and to a Senate Judiciary Committee on crime and prisons focused on detention of juveniles (Zimbardo, 1974). Its chair, Senator Birch Bayh, prepared a new law for federal prisons requiring juveniles in pre-trial detention to be housed separately from adult inmates (to prevent their being abused), based on the abuse reported in the Stanford Prison Experiment of its juveniles in the pre-trial detention facility of the Stanford jail.

A video documentary of the study, "Quiet Rage: the Stanford Prison Experiment," has been used extensively by many agencies within the civilian and military criminal justice system, as well as in shelters for abused women. It is also used to educate role-playing military interrogators in the Navy SEAR program (SURVIVAL, EVASION, and RESISTANCE) on the potential dangers of abusing their power against others who role-playing pretend spies and terrorists (Zimbardo, Personal communication, fall, 2003, Annapolis Naval College psychology staff).

The eerily direct parallels between the sadistic acts perpetrator by the Stanford Prison Experiment guard and the Abu Ghraib Prison guards, as well as the conclusions about situational forces dominating dispositional aspects of the guards' abusive behavior have propelled this research into the national dialogue. It is seen as a relevant contribution to understanding the multiple situational causes of such aberrant behavior. The situational analysis of the Stanford Prison Experiment redirects the search for blame from an exclusive focus on the character of an alleged "few bad apples" to systemic abuses that were inherent in the "bad barrel" of that corrupting prison environment.

Cited Research

Blass, T. (Ed.) ( 1999). Obedience to Authority: Current Perspectives on the Milgram Paradigm. Mahwah, NJ: Erlbaum.

Haney, C. & Zimbardo, P.G., (1998). The Past and Future of U.S. Prison Policy. Twenty-Five Years After the Stanford Prison Experiment. American Psychologist, Vol. 53, No. 7, pp. 709-727.

Milgram, S. (1974). Obedience to Authority. New York: Harper & Row.

Zimbardo, P. G. (1971). The power and pathology of imprisonment. Congressional Record. (Serial No. 15, October 25, 1971). Hearings before Subcommittee No. 3, of the Committee on the Judiciary, House of Representatives, Ninety-Second Congress, First Session on Corrections, Part II, Prisons, Prison Reform and Prisoner's Rights: California. Washington, DC: U.S. Government Printing Office.

Zimbardo, P. G. (1974). The detention and jailing of juveniles (Hearings before U. S. Senate Committee on the Judiciary Subcommittee to Investigate Juvenile Delinquency, 10, 11, 17, September, 1973). Washington, DC: U.S. Government Printing Office, 141-161.

Zimbardo, P. G., Haney, C., Banks, W. C., & Jaffe, D. (1973, April 8). The mind is a formidable jailer: A Pirandellian prison. The New York Times Magazine, Section 6, pp. 38, ff.

Zimbardo, P. G., Maslach, C., & Haney, C. (1999). Reflections on the Stanford Prison Experiment: Genesis, transformations, consequences. In T. Blass (Ed.), Obedience to Authority: Current Perspectives on the Milgram Paradigm. (pp. 193-237). Mahwah, NJ: Erlbaum.

American Psychological Association, June 8, 2004

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Stanford Prison Experiment

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Stanford Prison Experiment , a social psychology study in which college students became prisoners or guards in a simulated prison environment . The experiment, funded by the U.S. Office of Naval Research, took place at Stanford University in August 1971. It was intended to measure the effect of role-playing, labeling, and social expectations on behaviour over a period of two weeks. However, mistreatment of prisoners escalated so alarmingly that principal investigator Philip G. Zimbardo terminated the experiment after only six days.

More than 70 young men responded to an advertisement about a “psychological study of prison life,” and experimenters selected 24 applicants who were judged to be physically and mentally healthy. The paid subjects—they received $15 a day—were divided randomly into equal numbers of guards and prisoners. Guards were ordered not to physically abuse prisoners and were issued mirrored sunglasses that prevented any eye contact. Prisoners were “arrested” by actual police and handed over to the experimenters in a mock prison in the basement of a campus building. Prisoners were then subjected to indignities that were intended to simulate the environment of a real-life prison. In keeping with Zimbardo’s intention to create very quickly an “atmosphere of oppression,” each prisoner was made to wear a “dress” as a uniform and to carry a chain padlocked around one ankle. All participants were observed and videotaped by the experimenters.

On only the second day the prisoners staged a rebellion. Guards then worked out a system of rewards and punishments to manage the prisoners. Within the first four days, three prisoners had become so traumatized that they were released. Over the course of the experiment, some of the guards became cruel and tyrannical, while a number of the prisoners became depressed and disoriented. However, only after an outside observer came upon the scene and registered shock did Zimbardo conclude the experiment, less than a week after it had started.

The Stanford Prison Experiment immediately came under attack on methodological and ethical grounds. Zimbardo admitted that during the experiment he had sometimes felt more like a prison superintendent than a research psychologist. Later on, he claimed that the experiment’s “social forces and environmental contingencies” had led the guards to behave badly. However, others claimed that the original advertisement attracted people who were predisposed to authoritarianism . The most conspicuous challenge to the Stanford findings came decades later in the form of the BBC Prison Study, a differently organized experiment documented in a British Broadcasting Corporation series called The Experiment (2002). The BBC’s mock prisoners turned out to be more assertive than Zimbardo’s. The British experimenters called the Stanford experiment “a study of what happens when a powerful authority figure (Zimbardo) imposes tyranny.”

The Stanford Prison Experiment became widely known outside academia . It was the acknowledged inspiration for Das Experiment (2001), a German movie that was remade in the United States as the direct-to-video film The Experiment (2010). The Stanford Prison Experiment (2015) was created with Zimbardo’s active participation; the dramatic film more closely followed actual events.

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Table of Contents

Background and Objectives

In the 1960s and 70s, psychologist Philip Zimbardo conducted several notable social psychology experiments examining how social roles and situations can impact human behavior .

Zimbardo designed the Stanford Prison Experiment in 1971 to explore the psychology of imprisoning people. He aimed to study how participants reacted to being assigned randomized roles of prisoner and guard.

Zimbardo’s primary hypothesis was that the imposed social roles and environment of a prison would dominate the individual personalities of the participants, causing them to exhibit more extreme behaviors.

The experiment intended to demonstrate that situational variables can have a more powerful influence over behavior than inherent individual traits.

Zimbardo set up a simulated prison environment in the basement of Stanford University’s psychology building.

He recruited 18 male college students through a newspaper ad offering $15 per day to participate.

Although the participants had no abnormal psychological issues, Zimbardo hoped to provoke realistic responses by creating a believable mock prison.

The experiment planned to observe the participants’ interactions, emotions, and behaviors in this environment over a planned two-week study period.

Through this approach, Zimbardo sought to gain insight into the psychological mechanisms that make prisons dehumanizing environments.

Methodology

Zimbardo converted a corridor of the psychology department building into a simulated prison environment.

The experiment was monitored with video cameras and microphones. The participants were randomly assigned to be either “prisoners” or “guards” using a coin flip.

The “prisoners” were picked up by surprise at their homes by actual police officers, searched, handcuffed, and brought to the mock prison.

The prisoners were stripped naked, deloused, and given smocks and stocking caps to establish their powerless status.

Each prisoner was assigned an ID number to replace their name and lived in a small cell containing only a cot for sleeping.

The “guards” worked eight-hour shifts, with three guards working each shift. Guards wore military-style uniforms and reflector sunglasses to create an anonymous, authoritative appearance.

They carried handcuffs, whistles, and billy clubs. The guards followed protocols to maintain control, including bag searches, ID checks, and setting strict schedules.

However, they could otherwise run the prison however they wished and were told to demand total compliance from prisoners.

The study was scheduled to run for 14 days.

Zimbardo intended to observe how the participants interacted in these circumstances.

He took on the role of the prison superintendent, navigating how the study would proceed. Zimbardo encouraged the guards to create an oppressive atmosphere and break down the prisoners over time.

Findings and Analysis

The experiment quickly escalated out of control as the “guards” began ramping up their harassment and authoritarian measures, while the “prisoners” passively accepted the abuse.

On the second day of the experiment, the prisoners rebelled by barricading their cell doors and taunting the guards.

The guards responded by forcibly stripping the prisoners naked and removing their beds as punishment.

One prisoner developed acute emotional disturbance and had to be released after only 36 hours.

Over the next few days, the guards escalated their aggressive and dehumanizing tactics using psychological humiliation.

They set up privilege systems to make prisoners turn on each other.

Prisoners were forced to repeat their ID numbers and do meaningless chores and exercise.

Some prisoners began showing signs of depression and acute anxiety .

The guards and prisoner “#819” came into major conflict , with the prisoner launching a hunger strike.

Prisoner #819 was then subjected to further abuse.

Zimbardo interpreted the behavior results as arising from the assigned social roles and rules dominating over individual dispositions.

The prisoners became increasingly passive , depressed, and helpless as the study went on.

The phenomenon of one domineering guard nicknamed “John Wayne” emerged through the study procedures.

Zimbardo concluded the imposed prison environment crushed internal values and morals.

Criticisms and Ethical Concerns

The Stanford Prison Experiment has been widely criticized for being unscientific and unethical.

Critics point out there was no control group to compare against the prisoner and guard group.

The sample size of only 24 male participants was also too small to draw general conclusions about human behavior.

There are major ethical concerns about the amount of psychological distress inflicted on the participants.

The prisoners showed signs of anxiety, depression, and learned helplessness. Critics argue it was unethical to allow participants to continue suffering emotional harm.

The guards were encouraged to degrade the prisoners without oversight on their methods.

The experimenters became overinvolved as the study progressed rather than remaining neutral observers.

The experiment could not be conducted today with current ethical standards.

Today’s Institutional Review Boards would never allow vulnerable participants to be subjected to such dangerous psychological manipulation without proper informed consent.

Critics argue Zimbardo was irresponsible for encouraging aggression and abuse between participants.

The dramatic, uncontrolled nature of the study design would be prohibited by today’s more stringent safeguards.

Ultimately, the Stanford Prison Experiment revealed more about the problematic study procedures than any deep insights into human behavior.

While thought-provoking, the experiment is widely considered unethical and lacking in scientific rigor by today’s standards.

Legacy and Relevance Today

While the Stanford Prison Experiment faced deserved criticism, it left a legacy and continues to be referenced given the dramatics of the study.

Zimbardo’s experiment demonstrated how situational variables like social roles can override individual disposition to generate extreme behaviors.

The study shed light on how putting people in positions of power without oversight can lead to the abuse of authority.

The Stanford Prison Experiment is frequently cited when discussing the psychology of imprisonment.

The study showed how prisoners can become distressed and resigned in response to an oppressive environment.

It provided insight into how regimes like concentration camps can gain control through psychological manipulation.

However, the experiment’s scientific limitations mean its conclusions should be applied cautiously.

The study informed later research into prison conditions and supervisor/subordinate dynamics.

Modern replication attempts have used more rigorous methods and ethical standards.

However, the original experiment’s dramatic narrative keeps its themes relevant when examining topics like oppression, compliance, surveillance, and dehumanization.

Zimbardo’s prison study remains impactful despite its flaws, pioneering new areas of psychology research.

While controversial, it provided a warning about unconstrained authority that still resonates over 50 years later.

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The Stanford Prison Experiment 50 Years Later: A Conversation with Philip Zimbardo

In April 1971, a seemingly innocuous ad appeared in the classifieds of the Palo Alto Times : Male college students needed for psychological study of prison life. $15 per day for 1-2 weeks. In no time, more than 70 students volunteered, and 24 were chosen. Thus began the Stanford Prison Experiment (SPE), conducted inside Jordan Hall on the Stanford campus. Originally scheduled to last two weeks, it was ended early over concerns regarding the behavior of both “prisoners” and “guards.” Still today, the SPE spikes enormous interest. Movies and documentaries have been made, books published, and studies produced about those six days. It’s clear today the research would never be allowed, but it was motivated by genuine concern over the ethical issues surrounding prisons, compliance with authority, and the evil humans have proved capable of. What was learned and at what cost? What is still being learned?

The Stanford Historical Society sponsors a look back at the controversial study with its leader, social psychologist Philip Zimbardo , Stanford Professor Emeritus of Psychology. Zimbardo is joined in conversation by Paul Costello who served as the chief communications officer for the School of Medicine for 17 years. He retired from Stanford in January 2021.

This program is organized by the Stanford Historical Society and co-sponsored by the Department of Psychology at Stanford University.

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Image credit: Stanford Prison Experiment (Special Collections and University Archives, Stanford Libraries)

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Philip Zimbardo defends the Stanford Prison Experiment, his most famous work

What’s the scientific value of the Stanford Prison Experiment? Zimbardo responds to the new allegations against his work.

by Brian Resnick

For decades, the story of the famous Stanford Prison Experiment has gone like this: Stanford professor Philip Zimbardo assigned paid volunteers to be either inmates or guards in a simulated prison in the basement of the school‘s psychology building. Very quickly, the guards became cruel, and the prisoners more submissive and depressed. The situation grew chaotic, and the experiment, meant to last two weeks, had to be ended after five days.

The lesson drawn from the research was that situations can bring out the worst in people. That, in the absence of firm instructions of how to act, we’ll act in accordance to the roles we’re assigned. The tale, which was made into a feature film , has been a lens through which we can understand human-rights violations, like American soldier’s maltreatment of inmates at the Abu Ghraib in Iraq in the early 2000s.

This month, the scientific validity of the experiment was boldly challenged. In a thoroughly reported exposé on Medium, journalist Ben Blum found compelling evidence that the experiment wasn’t as naturalistic and un-manipulated by the experimenters as we’ve been told.

A recording from the experiment reveals that the “warden,” a research assistant, told a reluctant guard that “the guards have to know that every guard is going to be what we call a ‘tough guard.’” The warden implored the guard to act tough because “we hope will come out of the study is a very serious recommendation for [criminal justice] reform.” The implication being that if the guard didn’t play the part, the study would fail.

Additionally, one of the “prisoners” in the study told Blum that he was “acting” during a what was observed to be a mental breakdown.

These new findings don’t mean that everything that happened in the experiment was theater. The “prisoners” really did rebel at one point, and the “guards” were cruel. But the new evidence suggests that the main conclusion of the experiment — the one that has been republished in psychology textbooks for years — doesn’t necessarily hold up. Zimbardo stated over and over the behavior seen in the experiment was the result of their own minds conforming to a situation. The new evidence suggests there was a lot more going on.

I wrote a piece highlighting Blum’s exposé and putting the prison experiment in the larger context of psychology’s replication crisis. Our headline stated “we just learned it [the Stanford Prison Experiment] was a fraud.”

Fraud is a moral judgment. And Zimbardo, now a professor emeritus, wrote to Vox, unhappy with this characterization of his study. (You can Zimbardo’s full written response to the criticisms here .)

So I called Zimbardo up to ask about the evidence in Blum’s piece. I also wanted to know: As a scientist, what do you do when the narrative of your most famous work changes dramatically and spirals out of your own control?

The conversation was tense. At one point, Zimbardo threatened to hang up.

Zimbardo believes Blum (and Vox) got the story wrong. He says only one guard was prodded to act tougher. (We did not discuss Blum’s evidence that the “prisoners” in the experiment were held against their will, despite pleas to leave.)

After talking with him, the results of the prison experiment still seem unscientific and untrustworthy. It’s an interesting demonstration, but should enduring lessons in psychology be based off of it? I doubt it.

Here’s our conversation, which has been edited for length and clarity.

Brian Resnick

Here’s my understanding of the criticisms that have come to light recently about the Stanford Prison Experiment.

For years, the conclusion that has been drawn from the study was that circumstances can bring out the worst in people or encourage bad behavior. And when some people are given power, and some people are stripped of it, that fosters ugly behavior.

What’s comes to light — what I got out of that Ben Blum’s report — was that it might not have all been the circumstance. That these guards that you employed were possibly coached in some ways.

There’s audio. And for me, it sounded pretty compelling that the warden in your experiment, who I understand was an experimental collaborator — was calling out a guard for not being tough enough. [The warden told the guard, “The guards have to know that every guard is going to be what we call a ‘tough guard.’” Listen to the tape here .]

So does that not invalidate the conclusion?

Philip Zimbardo

Not at all!

And why not?

Because he’s talking to one guard who was doing nothing. These are people we’ve hired who are doing it for a salary, $15 a day, to play the role of guard. And Jaffe [the warden] picks on this guy because he is doing nothing. He’s sitting on the sideline, doing nothing, watching. He’s gotta earn his keep as a guard.

The point is telling a guard to be tough does not mean telling a guard to be mean, to be cruel, to be sadistic, which many of the guards became of their own volition playing the role of what they thought was a prison guard. So I reject your assumption entirely.

Here’s the description of the experiment as written on your website: It says “the guards made up their own set of rules which they carried into effect.” In another paper , you wrote that the guards’ behavior was left up “to each subject’s prior societal learning of the meaning of prisons.”

But here’s a different possibility: Do you think it is possible that some of these guards were acting to please you, to please the study, and to do something good for science?

Even without telling the guards to explicitly do something, they might have gotten the impression that it was important for them to play these roles. And they were compelled to because of your authority.

Some of them might, but I think most of them didn’t.

For many of them, it was simply a way to make $15 a day during a two-week summer break between summer school and the start of classes in September. It was nothing more than that. It was not wanting to help science.

Some of them were increasingly mean, cruel, and sadistic way beyond any definition of tough. Some of them were guards who simply enforced the rules. And some of them were “good guards” who never did anything abusive to the prisoners. So it’s not that the situation brought a single quality in the guard. It’s a mix.

The criticism that you’re raising, that Blum raised, that others are raising, is that we told the guards to do what they ended up doing. And therefore, [the results were due to] obedience to authority, and it’s not the evolution of cruel behavior in the situation of a prison-like environment.

And I reject that.

Is it possible that some of the “prisoners” in your experiment were acting, playing along?

Zero? How can you say zero?

Okay, I can’t say.

I mean, the point was they locked themselves in their cells, they ripped off their numbers, they’re yelling and cursing at the guards. So, yeah, they could be acting. But why would they be acting. ... What would they get out of that?

Blum quoted one of the prisoners, Douglas Korpi, who had a breakdown. Korpi told Blum that he was acting. That he was in the midsts of studying for the GREs and just really wanted to get out of the experiment. Korpi told Blum, “Anybody who is a clinician would know that I was faking.”

Brian, Brian, I’m telling you every fucking thing that Ben Blum said is a lie; it’s false.

Nothing Korpi said to Ben Blum has any truth, zero. Look at Quiet Rage [a documentary about the prison experiment], look at where he says, “I was overcome in that situation. I broke down, I lost control of myself.”

Retrospectively now, he’s ashamed of having broken down. So he says he “was studying the Graduate Record Exam, I was faking it, I wanted to show I could get out and liberate my colleagues,” etc, etc.

So he is the least reliable source of any information about the study, except he documents the power of the situation to get somebody who’s psychologically normal, 36 hours before, who in an experiment, knowing it’s an experiment, has an emotional “breakdown,” and had to be released.

Let’s say: Regardless of whether guards were coached or not...

Brian, I’m gonna stop you.

Can I finish the question?

A guard, a single guard, okay? When you say guards you’re slipping back into your assumption, you’re slipping back to be like Blum. A guard was coached to be tough, and end of sentence there.

[Note: As a reminder, the tape of the experiment quoted the Jaffe, the “warden,” who played a critical role in leading the experiment, as saying, “The guards have to know that every guard is going to be what we call a ‘tough guard.’” Also, as Blum discovered in the Stanford archives, Jaffe wrote in his notes , “I was given the responsibility of trying to elicit ‘tough-guard’ behavior.” Which, again, raises suspicions that the experiment wasn’t as naturalistic as the experimenters implied.]

What I want to ask is: What is the case that this experiment should be seen as anything more than an anecdote? I don’t think anyone denies its historical value. It’s an interesting demonstration. Ideas that generated from it are worthwhile to follow up on and to study more carefully. Do you think the experiment itself has a definitive scientific value? If so, what is it?

It depends what you mean by scientific value. From the beginning, I have always said it’s a demonstration. The only thing that makes it an experiment is the random assignment to prisoners and guards, that’s the independent variable. There is no control group. There’s no comparison group. So it doesn’t fit the standards of what it means to be “an experiment.” It’s a very powerful demonstration of a psychological phenomenon, and it has had relevance.

So, yes, if you want to call it anecdote, that’s one way to demean it. If you want to say, “Is it a scientifically valid conclusion?” I say ... it doesn’t have to be scientifically valid. It means it’s a conclusion drawn from this powerful, unique demonstration.

Would you agree, as a scientist, that an early demonstration of an idea is bound to be reinterpreted in time, bound to be reevaluated?

Oh, they should. The essence of science is you don’t believe anything until it has a) been replicated, or b) been critically evaluated, as the study is being done now. I’m hoping a positive consequence of all of this is a better, fuller appreciation of what happened in the Stanford prison study.

Let me just add one thing: There are many, many classic studies that are now all under attack. ... by psychologists from a very different domain. It’s curious.

I’ve talked to a lot of researchers who are interested in replication, and reevaluating past work. They want to correct the record. I think they’re scared about what happens to the credibility of science if they don’t scrutinize the classics.

And I wonder from your point of view, as a scientist, do you need to be okay with losing control of the narrative of your work as it gets reevaluated?

Of course. The moment, the moment any of it was published, the moment any of this was put online, which I did as soon as I could, I lost. ... You lose control of it. Once it’s out there it’s not in your head anymore. Once it’s out in any public forum, then, of course, I lost control of “the narrative.”

Is it a study with flaws? I was the first to admit that many, many years ago.

A study like the prison experiment might just be too big and complicated, with too many inputs, too many variables, to really nail down or understand a single, simple conclusion from it.

The single conclusion is a broad line: Human behavior, for many people, is much more under the influence of social situational variables than we had ever thought of before.

I will stand by that conclusion for the rest of my life, no matter what anyone says.

I’m just unsure if we have the evidence to say if it’s true or not.

There are other researchers who are trying to drill down more into understanding what turns bad behavior on and off. And I’m sure you’re not a fan of him, but Alexander Haslam — [a psychologist who has tried to replicate the prison experiment study, and an academic critic of Zimbardo’s conclusions]

Oh, God! ... no, no, no.

You don’t want to talk about him.

Yeah, okay, No, I don’t want to talk about [him] at all.

Well, the gist of what he and his colleagues are arguing is this: Social identity is a really powerful motivator. And it’s perhaps more influential than situational factors. And perhaps the guards in your experiment became cruel because your warden used his authority to foster a social identity within them. [Here’s a new paper with their latest arguments. ]

I reject that. No, no. That’s their shtick, that’s what they’re pushing.

You don’t assume good faith on their part?

I’m not saying good faith. That’s what their claim to fame is the importance of social identity.

Of course people have social identity. But, there’s also something called situational identity. In a particular situation, you begin to play a role. You are the boss, you are the foreman, you are the drill sergeant, you are the fraternity hazing master. And in that role, which is not the usual you, you begin to do something which is role-bound. ... This is what anybody in this role does. And your behavior then changes.

Is there experimental evidence outside the prison experiment that supports that view?

The view that situation can make a difference?

Yeah. There are plenty of examples in history and current events, but is that something we know as a fact, as an experimental fact?

I don’t know off the top of my head. ...

I’ve always said it’s an interaction. I’m an interactionist. What I’ve said, if you read any of my textbooks, it’s always an interaction between what people bring into a situation, which means genetics and personality, and what the situation brings out in you, which is a social/psychological power of some situations over others. And I will stand by that, my whole career depends on that.

It’s not like I’m mindlessly promoting the situation is dominating everybody.

What would you fear might happen if people stop believing in the integrity of the Stanford Prison Experiment?

The fear is they will lose an important conclusion about the nature of human behavior as being, to some extent, situationally influenced.

You’re afraid they’ll lose an important conclusion even though the study is just a demonstration?

You demonstrate gravity by throwing a ball up and seeing if it comes down. I think you’re insisting on a traditional view of what is scientific, what is a scientific experiment, what is a scientifically validated conclusion. And I am saying from the beginning the Stanford Prison Experiment is a unique and powerful demonstration of how social/situational variables can influence the behavior of some people, some of the time. That’s a very modest conclusion.

All of this controversy is happening now because you gave your notes and tapes from the prison experiment to the Stanford archives. That transparency is commendable. Do you regret it?

No, I don’t regret it. The reason I did it is to make it available for researchers, for anybody, and people have gone through it.

So again, the last thing in the world I need is for people to doubt my honesty, my professional credibility. That’s an attack on me personally, and that I reject and I’m arguing it’s absolutely wrong.

Is it okay if we just move on from the Stanford Prison Experiment? Like you said, it’s a demonstration. Maybe we need to ground our understanding of acts of evil in something a little bit more scientific, to be honest.

At this point, I don’t want anyone to reject that basic conclusion that I’ve said several times in this interview. I don’t want that to be rejected. I would love for there to be better, more scientific evaluation of this conclusion, rather than a bunch of bloggers saying, “We’re gonna shoot it down.”

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The Stanford Prison Experiment: The Power of the Situation

• First Online: 20 January 2024

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• Harry Perlstadt   ORCID: orcid.org/0000-0002-0233-0463 3  

Part of the book series: Clinical Sociology: Research and Practice ((CSRP))

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Philip Zimbardo is best known for his 1971 Stanford Prison Experiment (SPE). Early in his career, he conducted experiments in the psychology of deindividualization, in which a person in a group or crowd no longer acts as a responsible individual but is swept along and participates in antisocial actions. After moving to Stanford University, he began to focus on institutional power over the individual in group settings, such as long-term care facilities for the elderly and prisons. His research proposal for a simulated prison was approved by the Stanford University Human Subjects Research Review Committee in July 1971. He built a mock prison in the basement of the University’s psychology building and recruited college-aged male subjects to play prisoners and guards. The study began on Sunday, August 8th, and was to run for 2 weeks but ended on Friday morning August 13th. In less than a week, several of the mock guards hazed and brutalized the mock prisoners, some of whom found ways of coping, while others exhibited symptoms of mental breakdown.

The degree of civilization in a society can be judged by entering its prisons. — attributed to Fyodor Dostoevsky, The House of the Dead

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I wish to thank Chris Herrera, Jonathan K. Rosen, David Segal and Ruth Spivak for their comments on this chapter.

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Perlstadt, H. (2023). The Stanford Prison Experiment: The Power of the Situation. In: Assessing Social Science Research Ethics and Integrity. Clinical Sociology: Research and Practice. Springer, Cham. https://doi.org/10.1007/978-3-031-34538-8_8

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The mind is a formidable jailer

The quiet of a summer morning in Palo Alto, Calif.; was shattered by a screeching squad car siren as police swept through the city picking up college students in a surprise mass arrest. Each suspect was charged with a felony, warned of his constitutional rights, spread‐eagled against the car,

The following article is the result of a research project at Stanford University conducted by Philip G. Zirnbardo, professor of psychology, and three graduate‐student colleagues: W. Curtis Banks, Craig Haney and David Jaffe.

In prison, those things withheld from and denied to the prisoner become precisely what he wants most of all.

—Eldridge Cleaver, “Soul on Ice.”

Our sense of power is more vivid when we break a man's spirit than when we win his heart. —Eric Hoffer, “The Passionate State of Mind.”

Every prison that men build is built with bricks of shame,/ and bound with bars lest Christ should see how men their brothers maim.

—Oscar Wilde, “The Ballad of Reading Gaol.”

Wherever anyone is against his will that is him a prison. —Epictetus, “Discourses.” searched, handcuffed and carted off in the back seat of the squad car to the police station for booking.

After fingerprinting and the preparation of identification forms for his “jacket” (central information file), each prisoner was left isolated in a detention cell to wonder what he had done to get himself into this mess. After a while, he was blindfolded and transported to the “Stanford County Prison.” Here he began the process of becoming a prisoner—stripped naked, skin‐searched, deloused and issued a uniform, bedding, soap and towel.

The warden offered an impromptu welcome:

“As you probaby know, I'm your warden. All of you have shown that you are unable to function outside in the real world for one reason or another—that somehow you lack the responsibility of good citizens of this great country. We of this prison, your correctional staff, are going to help you learn what your responsibilities as citizens of this country are. Here are the rules. Sometime in the near future there will be a copy of the rules posted in each of the cells. We expect you to know them and to be able to recite them by number. If you follow all of these rules and keep your hands clean, repent for your misdeeds and show a proper attitude of penitence, you and I will get along just fine.”

There followed a reading of the 16 basic rules of prisoner conduct. “Rule Number One: Prisoners must remain silent during rest periods, after lights are out, during meals and whenever they are outside the prison yard. Two: Prisoners must eat at mealtimes and only at mealtimes. Three: Prisoners must not move, tamper, deface or damage walls, ceilings, windows, doors, or other prison property. … Seven: Prisoners must address each other by their ID number only. Eight: Prisoners must address the guards as ‘Mr. Correctional Officer.’ … Sixteen: Failure to obey any of the above rules may result in punishment.”

By late afternoon these youthful “first offenders” sat in dazed silence on the cots in their barren cells trying to make sense of the events that had transformed their lives so dramatically.

If the police arrests and processing were executed with customary detachment, however, there were some things that didn't fit. For these men were now part of a very unusual kind of prison, an experimental mock prison, created by social psychologists to study the effects of imprisonment upon volunteer research subjects. When we planned our two‐week‐long simulation of prison life, we sought to understand more about the process by which people called “prisoners” lose their liberty, civil rights, independence and privacy, while those called “guards” gain social power by accepting the responsibility for controlling and managing the lives of their dependent charges.

Why didn't we pursue this research in a real prison? First, prison systems are fortresses of secrecy, closed to impartial observation, and thereby immune to critical analysis from anyone not already part of the correctional authority. Second, in any real prison, it is impossible to separate what each individual brings into the prison from what the prison brings out in each person.

We populated our mock prison with a homogeneous group of people who could be considered “normal‐average” on the basis of clinical interviews and personality tests. Our participants (10 prisoners and 11 guards) were selected from more than 75 volunteers recruited through ads in the city and campus newspapers. The applicants were mostly college students from all over the United States and Canada who happened to be in the Stanford area during the summer and were attracted by the lure of earning $15 a day for participating in a study of prison life. We selected only those judged to be emotionally stable, physically healthy, mature, law‐abiding citizens.

This sample of average, middle‐class, Caucasian, college‐age males (plus one Oriental student) was arbitrarily divided by the flip of a coin. Half were randomly assigned to play the role of guards, the others of prisoners. There were no measurable differences between the guards and the prisoners at the start of the experiment. Although initially warned that as prisoners their privacy and other civil rights would be violated and that they might be subjected to harassment, every subject was completely confident of his ability to endure whatever the prison had to offer for the full two‐week experimental period. Each subject unhesitatingly agreed to give his “informed consent” to participate.

The prison was constructed in the basement of Stanford University's psychology building, which was deserted after the end of the summer‐school session. A long corridor was converted into the prison “yard” by partitioning off both ends. Three small laboratory rooms opening onto this corridor were made into cells by installing metal barred doors and replacing existing furniture with cots, three to a cell. Adjacent offices were refurnished as guards’ quarters, interview‐testing rooms and bedrooms for the “warden” (Jaffe) and the “superintendent” (Zimbardo). A concealed video camera and hidden microphones recorded much of the activity and conversation of guards and prisoners. The physical environment was one in which prisoners could always be observed by the staff, the only exception being when they were secluded in solitary confinement (a small, dark storage closet, labeled “The Hole”).

Our mock prison represented an attempt to simulate the psychological state of imprisonment in certain ways. We based our experiment on an indepth analysis of the prison situation, developed after hundreds of hours of discussion with Carlo Prescott (our ex‐con consultant), parole officers and correctional personnel, and after reviewing much of the existing literature on prisons and concentration camps.

“Real” prisoners typically report feeling powerless, arbitrarily controlled, dependent, frustrated, hopeless, anonymous, dehumanized and emasculated. It was not possible, pragmatically or ethically, to create such chronic states in volunteer subjects who realize that they are in an experiment for only a short time. Racism, physical brutality, indefinite confinement and enforced homosexuality were not features of our mock prison. But we did try to reproduce those elements of the prison experience that seemed most fundamental.

We promoted anonymity by seeking to minimize each prisoner's sense of uniqueness and prior identity. The prisoners wore smocks and nylon stocking caps; they had to use their ID numbers; their personal effects were removed and they were housed in barren cells. All of this made them appear similar to each other and indistinguishable to observers. Their smocks, which were like dresses, were worn without undergarments, causing the prisoners to be restrained in their physical actions and to move in ways that were more feminine than masculine. The prisoners were forced to obtain permission from the guard for routine and simple activities such as writing letters, smoking a cigarette or even going to the toilet; this elicited from them a childlike dependency.

Their quarters, though clean and neat, were small, stark and without esthetic appeal. The lack of windows resulted in poor air circulation, and persistent odors arose from the unwashed bodies of the prisoners. After 10 P.M. lockup, toilet privileges were denied, so prisoners who had to relieve themselves would have to urinate and defecate in buckets provided by the guards. Sometimes the guards refused permission to have them cleaned out, and this made the prison smell. Above all, “real” prisons are machines for playing tricks with the human conception of time. In our windowless prison, the prisoners often did not even know whether it was day or night. A few hours after falling asleep, they were roused by shrill whistles for their “count.” The ostensible purpose of the count was to provide a public test of the prisoners’ knowledge of the rules and of their ID numbers. But more important, the count, which occurred at least once on each of the three different guard shifts, provided a regular occasion for the guards to relate to the prisoners. Over the course of the study, the duration of the counts was spontaneously increased by the guards from their initial perfunctory 10 minutes to a seemingly interminable several hours. During these confrontations, guards who were bored could find ways to amuse themselves, ridiculing recalcitrant prisoners, enforcing arbitrary rules and openly exaggerating dissension among the prisoners.

The guards were also “deindividualized”: They wore identical khaki uniforms and silver reflector sunglasses that made eye contact with them impossible. Their symbols of power were billy clubs, whistles, handcuffs and the keys to the cells and the “main gate.” Although our guards received no formal training from us in how to be guards, for the most part they moved with apparent ease into their roles. The media had already provided them with ample models of prison guards to emulate.

Because we were as interested in the guards’ behavior as in the prisoners’, they were given considerable latitude to improvise and to develop strategies and tactics of prisoner management. Our guards were told that they must maintain “law and order” in this prison, that they were responsible for handling any trouble that might break out, and they were cautioned about the seriousness and potential dangers of the situation they were about to enter. Surprisingly, in most prison systems, “real” guards are not given much more psychological preparation or adequate training than this for what is one of the most complex, demanding and dangerous jobs our so ciety has to offer. They are expected to learn how to adjust to their new employment mostly from on‐the‐job experience, and from contacts with the “old bulls” during a survival‐of‐the‐fittest orientation period. According to an orientation manual for correctional officers at San Quentin, “the only way you really get to know San Quentin is through experience and time. Some of us take more time and must go through more experiences than others to accomplish this; some really never do get there.”

You cannot be a prisoner if no one will be your guard, and you cannot be a prison guard if no one takes you or your prison seriously. Therefore, over time a perverted symbiotic relationship developed. As the guards became more aggressive, prisoners became more passive; assertion by the guards led to dependency in the prisoners; self‐aggrandizement was met with self‐deprecation, authority with helplessness, and the counterpart of the guards’ sense of mastery and control was the depression and hopelessness witnessed in the prisoners. As these differences in behavior, mood and perception became more evident to all, the need for the now “righteously” powerful guards to rule the obviously inferior and powerless inmates became a sufficient reason to support almost any further indignity of man against man:

Guard K: “During the inspection, I went to cell 2 to mess up a bed which the prisoner had made and he grabbed me, screaming that he had just made it, and he wasn't going to let me mess it up. He grabbed my throat, and although he was laughing I was pretty scared. …I lashed out with my stick and hit him in the chin (although not very hard), and when I freed myself I became angry. I wanted to get back in the cell and have a go with him, since he attacked me when I was not ready.”

Guard M: “I was surprised at myself … I made them call each other names and clean the toilets out with their bare hands. I practically considered the prisoners cattle, and I kept thinking: ‘I have to watch out for them in case they try something.”

Guard A: “I was tired of seeing the prisoners in their rags and smelling the strong odors of their bodies that filled the cells. I watched them tear at each other on orders given by us. They didn't see it as an experiment. It was real and they were fighting to keep their identity. But we were always there to show them who was boss.”

Power takes as ingratitude the writhing of its victims. —Rabindranath Tagore, “Stray Birds.”

Because the first day passed without incident, we were surprised and totally unprepared for the rebellion that broke out on the morning of the second day. The prisoners removed their stocking caps, ripped off their numbers and barricaded themselves inside the cells by putting their beds against the doors. What should we do? The guards were very much upset because the prisoners also began to taunt and curse them to their faces. When the morning shift of guards came on, they were upset at the night shift who, they felt, must have been too permissive and too lenient. The guards had to handle the rebellion themselves, and what they did was startling to behold.

At first they insisted that reinforcements be called in. The two guards who were waiting on stand‐by call at home came in, and the night shift of guards voluntarily remained on duty (without extra pay) to bolster the morning shift. The guards met and decided to treat force with force. They got a fire extinguisher that shot a stream of skin‐chilling carbon dioxide and forced the prisoners away from the doors; they broke into each cell, stripped the prisoners naked, took the beds out, forced the prisoners who were the ringleaders into solitary confinement and generally began to harass and intimidate the prisoners.

After crushing the riot, the guards decided to head off further unrest by creating a privileged cell for those who were “good prisoners” and then, without explanation, switching some of the troublemakers into it and some of the good prisoners out into the other cells. The prisoner ringleaders could not trust these new ceilmates because they had not joined in the riot and might even be “snitches.” The prisoners never again acted in unity against the system. One of the leaders of the prisoner revolt later confided:

“If we had gotten together then, I think we could have taken over the place. But when I saw the revolt wasn't working, I decided to toe the line. Everyone settled into the same pattern. From then on, we were really controlled by the guards.”

It was after this episode that the guards really began to demonstrate their inventiveness in the application of arbitrary power. They made the prisoners obey petty, meaningless and often inconsistent rules, forced them to engage in tedious, useless work, such as moving cartons back and forth between closets and picking thorns out of their blankets for hours on end. (The guards had previously dragged the blankets through thorny bushes to create this disagreeable task.) Not only did the prisoners have to sing songs or laugh or refrain from smiling on command; they were also encouraged to curse and vilify each other publicly during some of the counts. They sounded off their numbers endlessly and were repeatedly made to do pushups, on occasion with a guard stepping on them or a prisoner sitting on them.

Slowly the prisoners became resigned to their fate and even behaved in ways that actually helped to justify their dehumanizing treatment at the hands of the guards. Analysis of the tape‐recorded private conversations between prisoners and of remarks made by them to interviewers revealed that fully half could be classified as nonsupportive of other prisoners. More dramatic, 85 per cent of the evaluative state ments by prisoners about their fellow prisoners were uncomplimentary and deprecating.

This should be taken in the context of an even more surprising result. What do you imagine the prisoners talked about when they were alone in their cells with each other, given a temporary respite from the continual harassment and surveillance by the guards? Girl friends, career plans, hobbies or politics?

No, their concerns were almost exclusively riveted to prison topics. Their monitored conversations revealed that only 10 per cent of the time was devoted to “outside” topics, while 90 per cent of the time they discussed escape plans, the awful food, grievances or ingratiation tactics to use with specific guards in order to get a cigarette, permission to go to the toilet or some other favor. Their obsession with these immediate survival concerns made talk about the past and future an idle luxury.

And this was not a minor point. So long as the prisoners did not get to know each other as people, they only extended the oppressiveness and reality of their life as prisoners. For the most part, each prisoner observed his fellow prisoners allowing the guards to humiliate them, acting like compliant sheep, carrying out mindless orders with total obedience and even being cursed by fellow prisoners (at a guard's command). Under such circumstances, how could a prisoner have respect for his fellows, or any self‐respect for what he obviously was becoming in the eyes of all those evaluating him?

Life is the art of being well deceived; and in order that the deception may succeed it must be habitual and uninterrupted. —William Hazlitt, “On Pedantry,” in “The Round Table.”

The combination of realism and symbolism in this experiment had fused to create a vivid illusion of imprisonment. The illusion merged inextricably with reality for at least some of the time for every individual in the situation. It was remarkable how readily we all slipped into our roles, temporarily gave up our identities and allowed these assigned roles and the social forces in the situation to guide, shape and eventually to control our freedom of thought and action.

But precisely where does one's “identity” end and one's “role” begin? When the private self and the public role behavior clash, what direction will attempts to impose consistency take? Consider the reactions of the parents, relatives and friends of the prisoners who visited their forlorn sons, brothers and lovers during two scheduled visitors’ hours. They were taught in short order that they were our guests, allowed the privilege of visiting only by complying with the regulations of the institution. They had to register, were made to wait half an hour, were told that only two visitors could see any one prisoner; the total visiting time was cut from an hour to only 10 minutes, they had to be under the surveillance of a guard, and before any parents could enter the visiting area, they had to discuss their son's case with the warden. Of course they complained about these arbitrary rules, but their conditioned, middle‐class reaction was to work within the system to appeal privately to the superintendent to make conditions better for their prisoners.

In less than 36 hours, we were forced to release prisoner 8612 because of extreme depression, disorganized thinking, uncontrollable crying and fits of rage. We did so reluctantly because we be lieved he was trying to “con” us—it was unimaginable that a volunteer prisoner in a mock prison could legitimately be suffering and disturbed to that extent. But then on each of the next three days another prisoner reacted with similar anxiety symptoms, and we were forced to terminate them, too. In a fifth case, a prisoner was released after developing a psychosomatic rash over his entire body (triggered by rejection of his parole appeal by the mock parole board). These men were simply unable to make an adequate adjustment to prison life. Those who endured the prison experience to the end could be distinguished from those who broke down and were released early in only one dimension—authoritarianism: On a psychological test designed to reveal a person's authoritarianism, those prisoners who had the highest scores were best able to function in this authoritarian prison environment.

If the authoritarian situation became a serious matter for the prisoners, it became even more serious—and sinister—for the guards. Typically, the guards insulted the prisoners, threatened them, were physically aggressive, used instruments (night sticks, fire extinguishers, etc.) to keep the prisoners in line and re ferred to them in impersonal, anonymous, deprecating ways: “Hey, you,” or “You [obscenity], 5401, come here.” From the first to the last day, there was a significant increase in the guards’ use of most of these domineering, abusive tactics.

Everyone and everything in the prison was defined by power. To be a guard who did not take advantage of this institutionally sanctioned use of power was to appear “weak,” “out of it,” “wired up by the prisoners,” or simply a deviant from the established norms of appropriate guard behavior. Using Erich Fromm's definition of sadism, as “the wish for absolute control over another living being,” all of the mock guards at one time or another during this study behaved sadistically toward the prisoners. Many of them reported —in their diaries, on criticalincident report forms and during post‐experimental interviews—being delighted in the new‐found power and control they exercised and sorry to see it relinquished at the end of the study.

Some of the guards reacted to the situation in the extreme and behaved with great hostility and cruelty in the forms of degradation they invented for the prisoners. But others were kinder; they occasionally did little favors for the prisoners, were reluctant to punish them, and avoided situations where prisoners were being harassed. The torment experienced by one of these good guards is obvious in his perceptive analysis of what it felt like to be responded to as a “guard”: “What made the experience most depressing for me was the fact that we were continually called upon to act in a way that just was contrary to what I really feel inside. I don't feel like I'm the type of person that would be a guard, just constantly giving out … and forcing people to do things, and pushing and lying —it just didn't seem like me, and to continually keep up and put on a face like that is just really one of the most oppressive things you can do. It's almost like a prison that you create yourself—you get into it, and it becomes almost the definition you make of yourself, it almost becomes like walls, and you want to break out and you want just to be able to tell everyone that this isn't really me at that's confined in there—I'm a person who wants to get out and show you that I am free, and I do have my own will, and I'm not the sadistic type of person that enjoys this kind of thing.”

Still, the behavior of these good guards seemed more motivated by a desire to be liked by everyone in the system than by a concern for the inmates’ welfare. No guard ever intervened in any direct way on behalf of the prisoners, ever interfered with the orders of the cruelest guards or ever openly complained about the subhuman quality of life that characterized this prison.

Perhaps the most devastating impact of the more hostile guards was their creation of a capricious, arbitrary environment. Over time the prisoners began to react passively. When our mock prisoners asked questions, they got answers about half the time, but the rest of the time they were insulted and punished—and it was not possible for them to predict which would be the outcome. As they began to “toe the line,” they stopped resisting, questioning and, indeed, almost ceased responding altogether. There was a general decrease in all categories of response as they learned the safest strategy to use in an unpredictable, threatening environment from which there is no physical escape—do nothing, except what is required. Act not, want not, feel not and you will not get into trouble in prisonlike situations.

And the only way to really make it with the bosses [in Texas prisons] is to withdraw into yourself, both mentally and physically—literally making yourself as small as possible. It's another way they dehumanize you. They want you to make no waves in prison and they want you to make no waves when you get out.

—Mike Middleton, ex‐con, The Christian Science Monitor.

Can it really be, you wonder, that intelligent, educated volunteers could have lost sight of the reality that they were merely acting a part in an elaborate game that would eventually end? There are many indications not only that they did, but that, in addition, so did we and so did other apparently sensible, responsible adults.

Prisoner 819, who had gone into a rage followed by an uncontrollable crying fit, was about to be prematurely released from the prison when a guard lined up the prisoners and had them chant in unison, “819 is a bad prisoner. Because of what 819 did to prison property we all must suffer. 819 is a bad prisoner.” Over and over again. When we realized 819 might be overhearing this, we rushed into the room where 819 was supposed to be resting, only to find him in tears, prepared to go back into the prison because he could not leave as long as the others thought he was a “bad prisoner.” Sick as he felt, he had to prove to them he was not a “bad” prisoner. He had to be persuaded that he was not a prisoner at all, that the others were also just students, that this was just an experiment and not a prison and the prison staff were only research psychologists. A report from the warden notes, “While I believe that it was necessary for staff [me] to enact the warden role, at least some of the time, I am startled by the ease with which I could turn off my sensitivity and concern for others for a cause.”

Consider our overreaction to the rumor of a mass escape plot that one of the guards claimed to have overheard. It went as follows: Prisoner 8612, previously released for emotional disturbance, was only faking. He was going to round up a bunch of his friends, and they would storm the prison right after visiting hours. Instead of collecting data on the pattern of rumor transmission, we made plans to maintain the security of our institution. After putting a confederate informer into the cell 8612 had occupied to get specific information about the escape plans, the superintendent went back to the Palo Alto Police Department to request transfer of our prisoners to the old city jail. His impassioned plea was only turned down at the last minute when the problem of insurance and city liability for our prisoners was raised by a city official. Angered at this lack of cooperation, the staff formulated another plan. Our jail was dismantled, the prisoners, chained and blindfolded, were carted off to a remote storage room. When the conspirators arrived, they would be told the study was over, their friends had been sent home, there was nothing left to liberate. After they left, we would redouble the security features of our prison making any fu ture escape attempts futile. We even planned to lure exprisoner 8612 back on some pretext and imprison him again, because he had been released on false pretenses! The rumor turned out to be just that — a full day had passed in which we collected little or no data, worked incredibly hard to tear down and then rebuild our prison. Our reaction, however, was as much one of relief and joy as of exhaustion and frustration.

When a former prison chaplain was invited to talk with the prisoners (the grievance committee had, requested church services), he puzzled everyone by disparaging each inmate for not having taken any constructive action in order to get released. “Don't you know you must have a lawyer in order to get bail, or to appeal the charges against you?” Several of them accepted” his invitation to contact their parents in order to secure the services of an attorney. The next night one of the parents stopped at the superintendent's office before visiting time and handed him the name and phone number of her cousin who was a public defender. She said that a priest had called her and suggested the need for a lawyer's services! We called the lawyer. He came, interviewed the prisoners, discussed sources of bail money and promised to return again after the weekend.

But perhaps the most telling account of the insidious development of this new reality, of the gradual Kafkaesque metamorphosis of good into evil, appears in excerpts from the diary of one of the guards, Guard A:

Prior to start of experiment: “As I am a pacifist and nonaggressive individual I cannot see a time when I might guard and/or maltreat other living things.”

After an orientation meeting: “Buying uniforms at the end of the meeting confirms the gamelike atmosphere of this thing. I doubt whether many of us share the expectations of ‘seriousness’ that the experimenters seem to have.”

First Day: “Feel sure that the prisoners will make fun of my appearance and I evolve my first basic strategy —mainly not to smile at anything they say or do which would be admitting it's all only a game. … At cell 3 I stop and setting my voice hard and low say to 5486, ‘What are you smiling at? ‘Nothing, Mr. Correctional Officer.’ ‘Well, see that you don't.’ (As I walk off I feel stupid.)”

Second Day: “5704 asked for a cigarette and I ignored him — because I am a nonsmoker and could not empathize. … Meanwhile since I was feeling empathetic towards 1037, I determined not to talk with him … after we had count and lights out [Guard D] and I held a loud conversation about going home to our, girl friends and what we were going to do to them.”

Third Day (preparing for the first visitors’ night): “After warning the prisoners not to make any complaints unless they wanted the visit terminated fast, we finally brought in the first parents. I made sure I was one of the guards on the yard, because this was my first chance for the type of manipulative power that I really like—being a very noticed figure with almost complete control over what is said or not. While the parents and prisoners sat in chairs, I sat on the end of the table dangling my feet and contradicting anything I felt like. This was the first part of the experiment I was really enjoying. … 817 is being obnoxious and bears watching?

Fourth Day: “… The psychologist rebukes me for handcuffing and blindfolding a prisoner before leaving the [counseling] office, and I resentfully reply that it is both necessary security and my business anyway.”

Fifth Day: “I harass ‘Serge’ who continues to stubbornly overrespond to all commands. I have singled him out for special abuse both because he begs for it and because I simply don't like him. The real trouble starts at dinner. The new prisoner (416) refuses to eat his sausage … we throw him into the Hole ordering him to hold sausages in each hand. We have a crisis of authority; this rebellious conduct potentially undermines the complete control we have over the others. We decide to play upon prisoner solidarity and tell the new one that all the others will be deprived of visitors if he does not eat his dinner. … I walk by and slam my stick into the Hole door. … I am very angry at this prisoner for causing discomfort and trouble for the others. I decided to forcefeed him, but he wouldn't eat. I let the food slide down his face. I didn't believe it was me doing it. I hated myself for making him eat but I hated him more for not eating.”

Sixth Day: “The experiment is over. I feel elated but am shocked to find some other guards disappointed somewhat becadse of the loss of money and some because they are enjoying themselves.”

We were no longer dealing with an intellectual exercise in which a hypothesis was being evaluated in the dispassionate manner dictated by the canons of the scientific method. We were caught up in the passion of the present, the suffering, the need to control people, not variables, the escalation of power and all of the unexpected things that were erupting around and within us. We had to end this experiment. So our planned two‐week simulation was aborted after only six (was it only six?) days and nights.

We've traveled too far, and our momentum has taken over; we move idly towards eternity, without possibility of reprieve or hope of explanation.

—Tom Stoppard, “Rosencrantz and Guildenstern Are Dead.”

Was it worth all the suffering just to prove what everyone knows—that some people are sadistic, others weak and prisons are not beds of roses? If that is all we demonstrated in this research, then it was certainly not worth the anguish. We believe there are many significant implications to be derived from this experience, only a few of which can be suggested here.

The potential social value of this study derives precisely from the fact that normal, healthy, educated young men could be so radically transformed under the institutional pressures of a “prison environment.” If this could happen in so short a time, without the excesses that are possible in real prisons, and if it could happen to the “cream‐of‐thecrop of American youth,” then one can only shudder to imagine what society is doing both to the actual guards and prisoners who are at this very moment participating in that unnatural “social experiment.”

The pathology observed in this study cannot be reasonably attributed to pre‐existing personality differences of the subjects, that option being eliminated by our, selection procedures and random assignment. Rather, the subjects’ abnormal social and personal reactions are best seen as a product of their transaction with an environment that supported the behavior that would be pathological in other settings, but was “appropriate” in this prison. Had we observed comparable reactions in a real prison, the psychiatrist undoubtedly would have been able to attribute any prisoner's behavior to character defects or personality maladjustment, while critics of the prison system would have been quick to label the guards as “psychopathic.” This tendency to locate the source of behavior disorders inside a particular person or group underestimates the power of situational forces.

Our colleague, David Rosenhan, has very convincingly shown that once a sane person (pretending to be insane) gets labeled as insane and committed to a mental hospital, it is the label that is the reality which is, treated and not the person. This dehumanizing tendency to respond to other people according to socially determined labels and often arbitrarily assigned roles is also apparent in a recent signed by Norina Jean Orlando to extend the ideas in our research.

Personnel from the staff of Elgin State Hospital in Illinois role‐played either mental patients or staff in a weekend simulation on a ward in the hospital. The mock mental patients soon displayed behavior indistinguishable from that we usually associate with the chronic pathological syndromes of actual mental patients: incessant pacing, uncontrollable weeping, depression, hostility, fights, stealing from each other, complaining. Many of the “mock staff” took advantage of their power to act in ways comparable to our mock guards by dehumanizing their powerless victims.

During a series of encounter debriefing sessions immediately after our experiment, we all had an opportunity to vent our strong feelings and to reflect upon the moral and ethical issues each of us faced, and we considered how we might react more morally in future “real‐life” analogues to this situation. Year‐long follow‐ups with our subjects via questionnaires, personal interviews and group reunions indicate that their mental anguish was transient and situation ally specific, but the selfknowledge gained has persisted.

For the most disturbing implication of our research comes from the parallels between what occurred in that basement mock prison and daily experiences in our own lives—and we presume yours. The physical institution of prison is but a concrete and steel metaphor for the existence of more pervasive, albeit less obvious, prisons of the mind that all of us daily create, populate and perpetuate. We speak here of the prisons of racism, sexism, despair, shyness, “neurotic hang‐ups” and the like. The social convention of marriage, as one example, becomes for many couples a state of im prisonmeht in which one partner agrees to be prisoner or guard, forcing or allowing the other to play the reciprocal role—invariably without making the contract explicit.

To what extent do we allow ourselves to become imprisoned by docilely accepting the roles others assign us or, indeed, choose to remain prisoners because being passive and dependent frees us from the need to act and be responsible for our actions? The prison of fear constructed in the delusions of the paranoid is no less confining or less real than the cell that every shy person erects to limit his own freedom in anxious anticipation of being ridiculed and rejected by his guards—often guards of his own making.

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Stanford Prison Experiments: Film #1

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Producer : Zimbardo, Philip G.

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Stanford Prison Experiment

• Quiet Rage: The Stanford Prison Experiment

Philip G. Zimbardo

Philip Zimbardo was born on March 23, 1933 in New York City. He attended Brooklyn College where he earned a B.A. in 1954, triple majoring in psychology, sociology and anthropology. He then went on to earn his M.A. in 1955 and his Ph.D. in 1959 from Yale University, both in psychology.

He taught briefly at Yale before becoming a psychology professor at New York University, where he taught until 1967. After a year of teaching at Columbia University, he became a faculty member at Stanford University in 1968.

Philip Zimbardo is perhaps best known for the Stanford Prison Experiment, conducted in the basement of the Stanford University psychology department in 1971. The participants in the study were 24 male college students who were randomly assigned to act either as "guards" or "prisoners" in the mock prison.

The study was initially slated to last two weeks, but had to be terminated after just six days because of the extreme reactions and behaviors of the participants. The guards began displaying cruel and sadistic behavior toward the prisoners, while the prisoners became depressed and hopeless.

Since the prison experiment, Zimbardo has continued to conduct research on a variety of topics including shyness, cult behavior and heroism. In 2002, Zimbardo was elected president of the American Psychological Association. After more than 50 years of teaching, Zimbardo retired from Stanford in 2003 but gave his last "Exploring Human Nature" lecture on March 7, 2007.

Today, he continues to work as the director of an organization he founded called the Heroic Imagination Project. The organization promotes research, education and media initiatives designed to inspire ordinary people to act as heroes and agents of social change.

The Rarely-Told True Story of Zimbardo’s Prison Experiment

Goodness, evil, and the power that may cause both..

Posted July 20, 2013 | Reviewed by Jessica Schrader

You don’t need to have a background in psychology to know about Zimbardo’s prison experiment. Depicted in movies, television, and of course all introductory psych textbooks, the true story is rarely told of what really happened in that famous and controversial experiment. When such iconic studies become part of psychology lore, their true story often gets buried in overly simplistic interpretations. Worse still, as in the case of the equally famous Milgram obedience studies , the findings become grossly distorted. The truth behind these studies will be revealed to the first time to American audiences in September of 2013, with the publication of Gina Perry’s brilliant book, Behind the Shock Machine .

Inspired by her work, I decided to go back to the original source of some of the social psych studies I’ve written and taught about for years (actually, decades). Having read the same textbook summaries, ethical discussions, and secondary sources as thousands of psychology professors and students in the past 40 years since the actual study's first publication, I thought it was time to see what really transpired in those prison cells that Zimbardo and his team built to explore the “Interpersonal Dynamics in a Simulated Prison.” Published in 1973, this landmark study in the very first volume of the International Journal of Criminology and Penology, describes in academic, yet compelling, terms the frightening events that transpired over the course of the six-day experiment. From personality questionnaires to follow-up interviews, audio and video recordings, and the first-person experience of the “prison superintendent” (none other than Zimbardo), we learn much more than you can ever typically expect to find in your average psychology article.

Of course, it will be impossible to do justice to the entire article here, and for more personal accounts and images from the study, you can consult many online resources including Zimbardo’s own website devoted to the study. You may even have seen Professor Zimbardo on television talking about the study, or taken the video course he hosted. If you haven’t, here’s the study in a nutshell. 21 Stanford undergrads were recruited for a two-week study, divided randomly into 10 “prisoners,” and 11 ”guards.” They were placed into a prison setting, where the prisoners occupied cells, and the guards watched over them. After six days, the experiment had spun out of control as simulation turned into reality, necessitating the early release of some prisoners. Most introductory psych texts use this experiment to demonstrate the “power of the situation,” and the fact that ordinary college students could become sadistic monsters (i.e. the guards) in the space of just a few short days. That guards and prisoners were randomly assigned to condition was a key fact that added to the validity of the conclusion. Discussions of the study’s ethics today state that it could never be done now, but the fact is that Zimbardo did submit the study for approval to his institutional review board, and it met the criteria of the time (for more on the study's ethics, see Zimbardo, 1973).

First off, you should recognize that this was no hokey, clearly fake situation (a problem that seemed to plague the Milgram experiments). The authors took elaborate precautions to recreate a realistic prison environment, from the uniforms to the furniture in the cells to the food and the schedule. As a result, “within what was a surprisingly short time, we witnessed a sample of normal, healthy American college men fractionate into a group of prison guards who seemed to derive pleasure from insulting, threatning, humiliating and dehumanizing their peers…” The guards, who showed no signs of being sadistic types, were able to provoke emotional breakdowns in prisoners “selected precisely” for their emotional stability .

The guards entered the study thinking that it was the prisoners whose behavior was being studied. They received training from the Zimbardo acting out his superintendent role and an undergraduate research assistant who was the “warden.” The prisoners were told that they would be asked to take on a prisoner role but given no other information other than the fact that they would be “arrested” and brought into the prison. Neither group had very specific instructions because the point of the experiment was to see how they adapted to their respective roles.

The prisoners were “arrested” by actual police officers, “booked,” and then stripped and put in a cell yard until they received their uniforms. The uniforms were more like hospital gowns, and the men wore no clothing underneath so that they would feel “emasculated.” These steps intentionally created a feeling of deidentification or loss of their own personal identities. Perhaps the only difference between the study prisoners and real prisoners is that the Stanford prisoners were paid, and could escape if they requested to be released from the study.

The experimenters collected almost everything that transpired as “data,” leaving them with an enormous amount of information to sift through, code, and analyze. At the end of it all, Zimbardo believed that their data supports and validates the anecdotal evidence given by ex-convicts of life in prison. All the students involved experienced changes in moods including intense negative affect, an overall pessimistic outlook, and greater and greater declines in their self-esteem . Although the prisoners and guards could interact in any way they wished, the “characteristic nature of their encounters tended to be negative, hostile, affrontive, and deumanising.” Prisoners became passive and guards barked commands and hurled insults (they were prohibited from any form of physical violence). Four prisoners had to be released as early as the second day due to extreme emotional reactions, and one developed a psychosomatic rash soon later which also required that he be released. What was particularly telling is that when the experiment was halted, the prisoners took the news like any prison escapees would—with glee. The guards were angry and distressed.

Not everyone reacted equally badly to their roles, though, and some guards were “tough but fair.” For the most part, these differential reactions couldn’t be predicted by the personal tests that the participants completed at the start of the study. Some of the prisoners high on “authoritarianism” coped better with prison life, but other than this, there were few indications from the individual data about who would conform and who would rebel or be unable to continue in their role.

The guards resorted to various forms of harassment short of physical punishment . They called prisoners by number, not name, and hurled streams of insults at them. The evening shift was the harshest—it was then that guards gave out the most commands and were most insulting and controlling.

For their part, the prisoners essentially stopped communicating with each other about anything other than prison life (talk which occupied 90% of all their private conversations). They tried to set up a grievance committee, develop escape plans, wonder what the other prisoners were doing, and express concern about being placed in solitary confinement. The dehumanization they experienced from the guards carried over to their own interpersonal interactions, and soon they started deprecating each other. When they had the opportunity to talk to a priest, they referred to themselves by number, not name, showing just how far their deidentification had penetrated. Fortunately, all of these bad experiences, including their negative moods, bounced back to normal after the end of the study. Their depression and stress were restricted entirely to the situation, further reinforcing the idea that the “power” of the situation to overwhelm individual differences in mood and personality.

The study highlights what social psychologists continually drum into our heads, which is that the situation can and does shape our behaviors, thoughts, and feelings at even the most private of levels. Yet, as Zimbardo points out, if this were a true prison, people would forget the dehumanizing and deindividuating nature of the environment and attribute everyone’s behavior (guards and prisoners) to personal disposition. The prisoners would not be seen as antisocial by nature and the guards as little better. Not everyone reacts similarly to even this harsh of an environment, of course, as people learn different coping methods to help them adapt, but the range is much smaller than we would imagine.

To sum up , the Zimbardo study sheds the harshest light of perhaps any research ever done on the nature of power and its pervasive corruptive powers.

From the standpoint of the guards, the pathology of power led them to exert an “unprecedented degree of control” that was “self-aggrandising” and “self-perpetuating.” Prisoners in the real world want to wrest back some of this control by any means necessary, and so when released, they “will take action to establish and assert a sense of power.”

While in prison, though, the loss of personal identity and control led the prisoners to adopt the pathological prisoner syndrome, a reaction that took several forms of coping strategies. They went through stages from disbelief to rebellion; when these didn’t work, they tried to work the system (the “grievance committee”). When those efforts to gain control failed, it was every man for himself as each tried to find ways to preserve their own self-interests and identity. For some, this meant further rebellion and for others it meant becoming excessively obedient, even to the point of siding with the guards against intransigent prisoners.

Zimbardo and his co-authors hoped that the emotional and human price of the study would provide a model for improvements in the penal system as a whole. You might not agree with his conclusion, but it’s a thought-provoking one, so I’ll offer it here: “… since prisoners and guards are locked into a dynamic, symbiotic relationship which is destructive to their human nature, guards are also society’s prisoners.”

Follow me on Twitter @swhitbo for daily updates on psychology, health, and aging . Feel free to join my Facebook group, " Fulfillment at Any Age ," to discuss today's post, or to ask further questions about this posting.

Copyright Susan Krauss Whitbourne, Ph.D. 2013.

Haney, C., Banks, C., & Zimbardo, P. (1973). Interpersonal dynamics in a simulated prison. International Journal of Criminology & Penology, 1(1), 69-97.

Zimbardo, P. G. (1973). On the ethics of intervention in human psychological research: With special reference to the Stanford prison experiment. Cognition, 2(2), 243-256. doi: 10.1016/0010-0277(72)90014-5

Susan Krauss Whitbourne, Ph.D. , is a Professor Emerita of Psychological and Brain Sciences at the University of Massachusetts Amherst. Her latest book is The Search for Fulfillment.

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