stanford prison experiment warden

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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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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The Real Lesson of the Stanford Prison Experiment

On the morning of August 17, 1971, nine young men in the Palo Alto area received visits from local police officers. While their neighbors looked on, the men were arrested for violating Penal Codes 211 and 459 (armed robbery and burglary), searched, handcuffed, and led into the rear of a waiting police car. The cars took them to a Palo Alto police station, where the men were booked, fingerprinted, moved to a holding cell, and blindfolded. Finally, they were transported to the Stanford County Prison—also known as the Stanford University psychology department.

They were willing participants in the Stanford Prison Experiment, one of the most controversial studies in the history of social psychology. (It’s the subject of a new film of the same name—a drama, not a documentary—starring Billy Crudup, of “Almost Famous,” as the lead investigator, Philip Zimbardo. It opens July 17th.) The study subjects, middle-class college students, had answered a questionnaire about their family backgrounds, physical- and mental-health histories, and social behavior, and had been deemed “normal”; a coin flip divided them into prisoners and guards. According to the lore that’s grown up around the experiment, the guards, with little to no instruction, began humiliating and psychologically abusing the prisoners within twenty-four hours of the study’s start. The prisoners, in turn, became submissive and depersonalized, taking the abuse and saying little in protest. The behavior of all involved was so extreme that the experiment, which was meant to last two weeks, was terminated after six days.

Less than a decade earlier, the Milgram obedience study had shown that ordinary people, if encouraged by an authority figure, were willing to shock their fellow-citizens with what they believed to be painful and potentially lethal levels of electricity. To many, the Stanford experiment underscored those findings, revealing the ease with which regular people, if given too much power, could transform into ruthless oppressors. Today, more than forty-five years later, many look to the study to make sense of events like the behavior of the guards at Abu Ghraib and America’s epidemic of police brutality. The Stanford Prison Experiment is cited as evidence of the atavistic impulses that lurk within us all; it’s said to show that, with a little nudge, we could all become tyrants.

And yet the lessons of the Stanford Prison Experiment aren’t so clear-cut. From the beginning, the study has been haunted by ambiguity. Even as it suggests that ordinary people harbor ugly potentialities, it also testifies to the way our circumstances shape our behavior. Was the study about our individual fallibility, or about broken institutions? Were its findings about prisons, specifically, or about life in general? What did the Stanford Prison Experiment really show?

The appeal of the experiment has a lot to do with its apparently simple setup: prisoners, guards, a fake jail, and some ground rules. But, in reality, the Stanford County Prison was a heavily manipulated environment, and the guards and prisoners acted in ways that were largely predetermined by how their roles were presented. To understand the meaning of the experiment, you have to understand that it wasn’t a blank slate; from the start, its goal was to evoke the experience of working and living in a brutal jail.

From the first, the guards’ priorities were set by Zimbardo. In a presentation to his Stanford colleagues shortly after the study’s conclusion, he described the procedures surrounding each prisoner’s arrival: each man was stripped and searched, “deloused,” and then given a uniform—a numbered gown, which Zimbardo called a “dress,” with a heavy bolted chain near the ankle, loose-fitting rubber sandals, and a cap made from a woman’s nylon stocking. “Real male prisoners don't wear dresses,” Zimbardo explained, “but real male prisoners, we have learned, do feel humiliated, do feel emasculated, and we thought we could produce the same effects very quickly by putting men in a dress without any underclothes.” The stocking caps were in lieu of shaving the prisoner’s heads. (The guards wore khaki uniforms and were given whistles, nightsticks, and mirrored sunglasses inspired by a prison guard in the movie “Cool Hand Luke.”)

Often, the guards operated without explicit, moment-to-moment instructions. But that didn’t mean that they were fully autonomous: Zimbardo himself took part in the experiment, playing the role of the prison superintendent. (The prison’s “warden” was also a researcher.) /Occasionally, disputes between prisoner and guards got out of hand, violating an explicit injunction against physical force that both prisoners and guards had read prior to enrolling in the study. When the “superintendent” and “warden” overlooked these incidents, the message to the guards was clear: all is well; keep going as you are. The participants knew that an audience was watching, and so a lack of feedback could be read as tacit approval. And the sense of being watched may also have encouraged them to perform. Dave Eshelman, one of the guards, recalled that he “consciously created” his guard persona. “I was in all kinds of drama productions in high school and college. It was something I was very familiar with: to take on another personality before you step out on the stage,” Eshelman said. In fact, he continued, “I was kind of running my own experiment in there, by saying, ‘How far can I push these things and how much abuse will these people take before they say, ‘Knock it off?’ ”

Other, more subtle factors also shaped the experiment. It’s often said that the study participants were ordinary guys—and they were, indeed, determined to be “normal” and healthy by a battery of tests. But they were also a self-selected group who responded to a newspaper advertisement seeking volunteers for “a psychological study of prison life.” In a 2007 study, the psychologists Thomas Carnahan and Sam McFarland asked whether that wording itself may have stacked the odds. They recreated the original ad, and then ran a separate ad omitting the phrase “prison life.” They found that the people who responded to the two ads scored differently on a set of psychological tests. Those who thought that they would be participating in a prison study had significantly higher levels of aggressiveness, authoritarianism, Machiavellianism, narcissism, and social dominance, and they scored lower on measures of empathy and altruism.

Moreover, even within that self-selected sample, behavioral patterns were far from homogeneous. Much of the study’s cachet depends on the idea that the students responded en masse, giving up their individual identities to become submissive “prisoners” and tyrannical “guards.” But, in fact, the participants responded to the prison environment in all sorts of ways. While some guard shifts were especially cruel, others remained humane. Many of the supposedly passive prisoners rebelled. Richard Yacco, a prisoner, remembered “resisting what one guard was telling me to do and being willing to go into solitary confinement. As prisoners, we developed solidarity—we realized that we could join together and do passive resistance and cause some problems.”

What emerges from these details isn’t a perfectly lucid photograph but an ambiguous watercolor. While it’s true that some guards and prisoners behaved in alarming ways, it’s also the case that their environment was designed to encourage—and, in some cases, to require—those behaviors. Zimbardo himself has always been forthcoming about the details and the nature of his prison experiment: he thoroughly explained the setup in his original study and, in an early write-up , in which the experiment was described in broad strokes only, he pointed out that only “about a third of the guards became tyrannical in their arbitrary use of power.” (That’s about four people in total.) So how did the myth of the Stanford Prison Experiment—“Lord of the Flies” in the psych lab—come to diverge so profoundly from the reality?

In part, Zimbardo’s earliest statements about the experiment are to blame. In October, 1971, soon after the study’s completion—and before a single methodologically and analytically rigorous result had been published—Zimbardo was asked to testify before Congress about prison reform. His dramatic testimony , even as it clearly explained how the experiment worked, also allowed listeners to overlook how coercive the environment really was. He described the study as “an attempt to understand just what it means psychologically to be a prisoner or a prison guard.” But he also emphasized that the students in the study had been “the cream of the crop of this generation,” and said that the guards were given no specific instructions, and left free to make “up their own rules for maintaining law, order, and respect.” In explaining the results, he said that the “majority” of participants found themselves “no longer able to clearly differentiate between role-playing and self,” and that, in the six days the study took to unfold, “the experience of imprisonment undid, although temporarily, a lifetime of learning; human values were suspended, self-concepts were challenged, and the ugliest, most base, pathological side of human nature surfaced.” In describing another, related study and its implications for prison life, he said that “the mere act of assigning labels to people, calling some people prisoners and others guards, is sufficient to elicit pathological behavior.”

Zimbardo released video to NBC, which ran a feature on November 26, 1971. An article ran in the Times Magazine in April of 1973. In various ways, these accounts reiterated the claim that relatively small changes in circumstances could turn the best and brightest into monsters or depersonalized serfs. By the time Zimbardo published a formal paper about the study , in a 1973 issue of the International Journal of Crim__i__nology and Penology , a streamlined and unequivocal version of events had become entrenched in the national consciousness—so much so that a 1975 methodological critique fell largely on deaf ears.

Forty years later, Zimbardo still doesn’t shy away from popular attention. He served as a consultant on the new film, which follows his original study in detail, relying on direct transcripts from the experimental recordings and taking few dramatic liberties. In many ways, the film is critical of the study: Crudup plays Zimbardo as an overzealous researcher overstepping his bounds, trying to create a very specific outcome among the students he observes. The filmmakers even underscore the flimsiness of the experimental design, inserting characters who point out that Zimbardo is not a disinterested observer. They highlight a real-life conversation in which another psychologist asks Zimbardo whether he has an “independent variable.” In describing the study to his Stanford colleagues shortly after it ended, Zimbardo recalled that conversation: “To my surprise, I got really angry at him,” he said. “The security of my men and the stability of my prison was at stake, and I have to contend with this bleeding-heart, liberal, academic, effete dingdong whose only concern was for a ridiculous thing like an independent variable. The next thing he’d be asking me about was rehabilitation programs, the dummy! It wasn’t until sometime later that I realized how far into the experiment I was at that point.”

In a broad sense, the film reaffirms the opinion of John Mark, one of the guards, who, looking back, has said that Zimbardo’s interpretation of events was too shaped by his expectations to be meaningful: “He wanted to be able to say that college students, people from middle-class backgrounds ... will turn on each other just because they’re given a role and given power. Based on my experience, and what I saw and what I felt, I think that was a real stretch.”

If the Stanford Prison Experiment had simulated a less brutal environment, would the prisoners and guards have acted differently? In December, 2001 , two psychologists, Stephen Reicher and Alexander Haslam, tried to find out. They worked with the documentaries unit of the BBC to partially recreate Zimbardo’s setup over the course of an eight-day experiment. Their guards also had uniforms, and were given latitude to dole out rewards and punishments; their prisoners were placed in three-person cells that followed the layout of the Stanford County Jail almost exactly. The main difference was that, in this prison, the preset expectations were gone. The guards were asked to come up with rules prior to the prisoners’ arrival, and were told only to make the prison run smoothly. (The BBC Prison Study, as it came to be called, differed from the Stanford experiment in a few other ways, including prisoner dress; for a while, moreover, the prisoners were told that they could become guards through good behavior, although, on the third day, that offer was revoked, and the roles were made permanent.)

Within the first few days of the BBC study, it became clear that the guards weren’t cohering as a group. “Several guards were wary of assuming and exerting their authority,” the researchers wrote. The prisoners, on the other hand, developed a collective identity. In a change from the Stanford study, the psychologists asked each participant to complete a daily survey that measured the degree to which he felt solidarity with his group; it showed that, as the guards grew further apart, the prisoners were growing closer together. On the fourth day, three cellmates decided to test their luck. At lunchtime, one threw his plate down and demanded better food, another asked to smoke, and the third asked for medical attention for a blister on his foot. The guards became disorganized; one even offered the smoker a cigarette. Reicher and Haslam reported that, after the prisoners returned to their cells, they “literally danced with joy.” (“That was fucking sweet,” one prisoner remarked.) Soon, more prisoners began to challenge the guards. They acted out during roll call, complained about the food, and talked back. At the end of the sixth day, the three insubordinate cellmates broke out and occupied the guards’ quarters. “At this point,” the researchers wrote, “the guards’ regime was seen by all to be unworkable and at an end.”

Taken together, these two studies don’t suggest that we all have an innate capacity for tyranny or victimhood. Instead, they suggest that our behavior largely conforms to our preconceived expectations. All else being equal, we act as we think we’re expected to act—especially if that expectation comes from above. Suggest, as the Stanford setup did, that we should behave in stereotypical tough-guard fashion, and we strive to fit that role. Tell us, as the BBC experimenters did, that we shouldn’t give up hope of social mobility, and we act accordingly.

This understanding might seem to diminish the power of the Stanford Prison Experiment. But, in fact, it sharpens and clarifies the study’s meaning. Last weekend brought the tragic news of Kalief Browder’s suicide . At sixteen, Browder was arrested, in the Bronx, for allegedly stealing a backpack; after the arrest, he was imprisoned at Rikers for three years without trial . (Ultimately, the case against him was dismissed.) While at Rikers, Browder was the object of violence from both prisoners and guards, some of which was captured on video . It’s possible to think that prisons are the way they are because human nature tends toward the pathological. But the Stanford Prison Experiment suggests that extreme behavior flows from extreme institutions. Prisons aren’t blank slates. Guards do indeed self-select into their jobs, as Zimbardo’s students self-selected into a study of prison life. Like Zimbardo’s men, they are bombarded with expectations from the first and shaped by preëxisting norms and patterns of behavior. The lesson of Stanford isn’t that any random human being is capable of descending into sadism and tyranny. It’s that certain institutions and environments demand those behaviors—and, perhaps, can change them.

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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."

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)

50 Years On: What We've Learned From the Stanford Prison Experiment

The experiment generated important research into unexplored territories..

Posted August 16, 2021 | Reviewed by Tyler Woods

• What Is Shyness?
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• I developed 3 new areas of research after the Stanford prison experiment (SPE): good and evil, time perspective, and shyness.
• The SPE was closed down after 6 days because the "guards" became so brutal and as Superintendent, I was too caught up in my role.
• The Heroic Imagination Project teaches people how to be Everyday Heroes and take effective actions in challenging situations.

Fifty years ago this month I conducted a research experiment that could have been a blight to my career . Instead, what has become known as the Stanford prison experiment (SPE) drove me to extensively pursue the question: Why do good people do evil things? After three decades of research on this subject, I recorded my findings in The Lucifer Effect: Understanding How Good People Turn Evil (Random House, 2007).

But the SPE also led me to research three new topics that hadn’t previously been studied:

1) Heroism: Why, in difficult situations, some people heroically step forward to help others, oftentimes complete strangers, while others stand by and watch.

2) Time Perspective: The psychological time warp experienced by participants of the SPE—not knowing if it was day or night or what day it was—led to my research in people’s individual time perspectives and how these affect our lives.

3) Shyness : Rethinking shyness as a self-imposed psychological prison led me to conduct research on shyness in adults, and then create a clinic in the community designed to cure shyness.

The Experiment in a Nutshell

In August 1971, I led a team of researchers at Stanford University to determine the psychological effects of being a guard or a prisoner. The study was funded by the US Office of Naval Research as both the US Navy and the US Marine Corps were interested in the causes of conflict between military guards and prisoners. In the study, 24 normal college students were randomly assigned to play the role of guard or inmate for two weeks in a simulated prison located in the basement of the Stanford Psychology Department building. But the guards quickly became so brutal, and I had become so caught up in my role as Superintendent, that I shut down the experiment after only six days.

Challenging the Truth

There seem to be powerful silent barriers to dealing with new truths emanating from psychological laboratories and field experiments that tell us things about how the mind works, which challenge our basic assumptions. We want to believe our decisions are wisely informed, that our actions are rational, that our personal conscience buffers us against tyrannical authorities. Moreover, we want to believe in the dominating influence of our good character despite social circumstances. Yes, those personal beliefs are sometimes true, but often they are not, and rigidly defending them can get us in trouble individually and collectively. Let’s see how.

Denial and Finger Pointing

When we discover two or three ordinary American citizens administered extreme electric shocks to an innocent victim on the relentless commands of a heartless authority, we say, “no way, not me.” Yale University psychologist Stanley Milgram’s obedience to authority research has been in the public arena for decades, yet we ignore its message of the power of unjust authority in undercutting our moral conscience. Similarly, the SPE research made vivid the power of hostile situational forces in overwhelming dispositional tendencies toward compassion and human dignity. Still, many who insist on honoring the dominance of character over circumstance reject its situational power message.

In 2004, people around the world witnessed online photos of horrific actions of American Military Police guards in Iraq’s Abu Ghraib Prison against prisoners in their charge. It was portrayed as the work of a “few bad apples” according to military brass and Bush administration spokespeople. I publicly challenged this traditional focus on individual dispositions by portraying American servicemen as good apples that were forced to operate in a Bad Barrel (the Situation) created by Bad Barrel Makers (the System).

I became an expert witness in the defense of the Staff Sergeant in charge of the night shift, where all the abuses took place. In that capacity, I had personal access to the defendant, to all 1,000 photos and videos, to all dozen military investigations, and more. It was sufficient to validate my view of that prison as a replica of the Stanford prison experiment on steroids, and of my defendant, Chip Frederick, as really a Good Apple corrupted by being forced to function for 12 hours every night for many months in the worst barrel imaginable. My situation-based testimony to the military Court Martial hearings helped reduce the severity of his sentence from 15 years down to only four years.

The January 6, 2021 insurrection is a recent example of some Good Apples being corrupted by a Bad Barrel. In this case, the Bad Barrel is the insidiousness of fascism led by the former president and other fraudulent politicians as well as media personalities. These “leaders” have been generously dumping poison in the Barrel and over the Apples with lies that feed the Apples’ deepest fears.

“The Stanford Prison Experiment” Film

In 2015, The Stanford Prison Experiment was made into a film starring Billy Crudup as me and Olivia Thrilby as Christina Maslach, the whistle-blowing graduate student (whom I later married) who pointed out the experiment had gone awry and had changed me to such a degree that she didn’t know who I was anymore. Her personal challenge led me to end the study the next day. The film received two awards at the Sundance Film Festival: best screenwriting and best science feature.

The Stanford Prison Experiment movie enables viewers to look through the observation window as if they were part of the prison staff watching this remarkable drama slowly unfold, and simultaneously observe those observers as well. They are witnesses to the gradual transformations taking place, hour by hour, day by day, and guard shift by guard shift. Viewers see what readers of The Lucifer Effect book account can only imagine. As these young students become the characters inhabited in their roles and dressed in their costumes, as prisoners or guards, a Pirandellian drama emerges.

The fixed line between Good, like us, and Evil, like them, is relentlessly blurred as it becomes ever more permeable. Ordinary people soon slip into doing extraordinarily bad things to other people, who are actually just like them except for a random coin flip. Other healthy people soon get sick mentally, being unable to cope with the learned helplessness imposed on them in that unique, unfamiliar setting. They do not offer comfort to their buddies as they break down, nor do those who adopt a “good guard” persona ever do anything to limit the sadistic excesses of the cruel guards heading their shifts.

Finally, the movie also tracks the emotional changes in the lead character (me) as his compassion and intellectual curiosity get distilled and submerged over time. The initial roles of research creator and objective observer are dominated by power and insensitivity to prisoners' suffering in the new role of Prison Superintendent.

Visit the official Stanford Prison Experiment website to learn more about the experiment.

Heroic Imagination

I should add that, along with continuing research in time perspectives and time perspective therapy , my new mission in life has been to empower everyone to wisely resist negative situational forces and evil by becoming Everyday Heroes in Training. Our non-profit Heroic Imagination Project (HIP) teaches ordinary people how to stand up, speak out and take effective actions in challenging situations in their lives.

Rosemary K.M. Sword and Philip Zimbardo are authors, along with Richard M. Sword, of The Time Cure: Overcoming PTSD with the New Psychology of Time Perspective Therapy.

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Chapter 4: Understanding and Influencing Others

Back to chapter, the stanford prison experiment, previous video 4.2: fundamental attribution error, next video 4.4: conformity.

There’s a dark side to the summer of 1971. Police “arrested” a number of college students who responded to an ad seeking volunteers for a psychological study of prison life.

Little did they know, in the basement of the Stanford Psychology Department, they were about to embark upon one of the most famous and controversial psychological studies: The Stanford Prison Experiment, led by Philip Zimbardo and colleagues.

After filling out an informational questionnaire, participants were randomly assigned to one of two groups: Prisoners—who were realistically picked up and booked by police—or Guards, who were in direct control of the inmates.

Depending on the assignment, they were dressed to fit their role —a set of expectations defining how those in the social position should behave.

For example, each guard was given a nightstick and whistle, along with mirrored aviator glasses, to emphasize their status and authority.

In addition, two researchers were present and oversaw the day-to-day operations: the lead experimenter, Zimbardo, acted as the prison superintendent, while another researcher, David Jaffe, was the Warden.

During one orientation session for the guards, Zimbardo vaguely outlined behaviors that they should conform with, like limiting the prisoners’ freedom and using their power to evoke fear and dominate non-violently.

In a follow-up session, the Warden provided more explicit directions to encourage the creation of a prison environment, for the collective good of the experiment.

With the correctional authorities in place, the prisoners entered the mock jail, which contained three cells and a closet for solitary confinement. They were stripped down, immediately degraded, and blindfolded to confuse them. Also, as part of their assigned role, they were outfitted in numbered gowns and nylon-stocking caps to depersonalize them.

On the second day, the prisoners started to rebel by blockading the cell door with the bed. As punishment, the ring leader was placed in confinement. This event precipitated the guards now turning on the other inmates, and the level of cruelty escalated.

Several guards… but not all …upped their performance to act tough—to fit the preconceived expectations of their label—all under the watchful eyes of the Warden and Superintendent. These leaders promoted toughness as a shared attribute of conforming to the in-group to achieve the goal of exposing the toxicity of the penal system.

Due to the increased and creative oppression placed on the prisoners, the experiment was terminated early, after six days instead of two weeks.

Ultimately, the guards behaved in a stereotypical tough-guy manner, striving to fit the normative guidance they were given. Sometimes, toxic situations can bring out the worst in someone, especially in cases where the individual identifies with a leader and the group’s collective cause.

The famous and controversial Stanford Prison Experiment , conducted by social psychologist Philip Zimbardo and his colleagues at Stanford University, demonstrated the power of social roles, social norms, and scripts.

Social Roles

One major social determinant of human behavior is our social role— a pattern of behavior that is expected of a person in a given setting or group (Hare, 2003). Each one of us has several social roles. You may be, at the same time, a student, a parent, an aspiring teacher, a son or daughter, a spouse, and a lifeguard. How do these social roles influence your behavior? Social roles are defined by culturally shared knowledge. That is, nearly everyone in a given culture knows what behavior is expected of a person in a given role. For example, what is the social role for a student? If you look around a college classroom you will likely see students engaging in studious behavior, taking notes, listening to the professor, reading the textbook, and sitting quietly at their desks. Of course, you may see students deviating from the expected studious behavior such as texting on their phones or using Facebook on their laptops, but in all cases, the students that you observe are attending class—a part of the social role of students.

Social roles, and our related behavior, can vary across different settings. How do you behave when you are engaging in the role of son or daughter and attending a family function? Now imagine how you behave when you are engaged in the role of employee at your workplace. It is very likely that your behavior will be different. Perhaps you are more relaxed and outgoing with your family, making jokes and doing silly things. But at your workplace you might speak more professionally, and although you may be friendly, you are also serious and focused on getting the work completed. These are examples of how our social roles influence and often dictate our behavior to the extent that identity and personality can vary with context (that is, in different social groups; Malloy, Albright, Kenny, Agatstein, & Winquist, 1997).

Social Norms

As discussed previously, social roles are defined by a culture’s shared knowledge of what is expected behavior of an individual in a specific role. This shared knowledge comes from social norms—a group’s expectations of what is appropriate and acceptable behavior for its members—how they are supposed to behave and think (Deutsch & Gerard, 1955; Berkowitz, 2004). How are we expected to act? What are we expected to talk about? What are we expected to wear? In our discussion of social roles, we noted that colleges have social norms for students’ behavior in the role of student and workplaces have social norms for employees’ behaviors in the role of employee. Social norms are everywhere including in families, gangs, and on social media outlets. 

Because of social roles, people tend to know what behavior is expected of them in specific, familiar settings. A script is a person’s knowledge about the sequence of events expected in a specific setting (Schank & Abelson, 1977). How do you act on the first day of school, when you walk into an elevator, or are at a restaurant? For example, at a restaurant in the United States, if we want the server’s attention, we try to make eye contact. In Brazil, you would make the sound “psst” to get the server’s attention. You can see the cultural differences in scripts. To an American, saying “psst” to a server might seem rude, yet to a Brazilian, trying to make eye contact might not seem an effective strategy. Scripts are important sources of information to guide behavior in given situations. Can you imagine being in an unfamiliar situation and not having a script for how to behave? This could be uncomfortable and confusing. How could you find out about social norms in an unfamiliar culture?

Zimbardo’s Stanford Prison Experiment

In the summer of 1971, an advertisement was placed in a California newspaper asking for male volunteers to participate in a study about the psychological effects of prison life. More than 70 men volunteered, and these volunteers then underwent psychological testing to eliminate candidates who had underlying psychiatric issues, medical issues, or a history of crime or drug abuse. The pool of volunteers was whittled down to 24 healthy male college students. Each student was paid $15 per day and was randomly assigned to play the role of either a prisoner or a guard in the study. Based on what you have learned about research methods, why is it important that participants were randomly assigned?

A mock prison was constructed in the basement of the psychology building at Stanford. Participants assigned to play the role of prisoners were “arrested” at their homes by Palo Alto police officers, booked at a police station, and subsequently taken to the mock prison. The experiment was scheduled to run for several weeks. To the surprise of the researchers, both the “prisoners” and “guards” assumed their roles with zeal. In fact, on day 2, some of the prisoners revolted, and the guards quelled the rebellion by threatening the prisoners with night sticks. In a relatively short time, the guards came to harass the prisoners in an increasingly sadistic manner, through a complete lack of privacy, lack of basic comforts such as mattresses to sleep on, and through degrading chores and late-night counts.

The prisoners, in turn, began to show signs of severe anxiety and hopelessness—they began tolerating the guards’ abuse. Even the Stanford professor who designed the study and was the head researcher, Philip Zimbardo, found himself acting as if the prison was real and his role, as prison supervisor, was real as well. After only six days, the experiment had to be ended due to the participants’ deteriorating behavior. 

The Stanford prison experiment demonstrated the power of social roles, norms, and scripts in affecting human behavior. The guards and prisoners enacted their social roles by engaging in behaviors appropriate to the roles: The guards gave orders and the prisoners followed orders. Social norms require guards to be authoritarian (such behavior was reinforced; see Haslam, Reicher, & Van Bavel, 2018) and prisoners to be submissive. When prisoners rebelled, they violated these social norms, which led to upheaval. The specific acts engaged by the guards and the prisoners derived from scripts. For example, guards degraded the prisoners by forcing them do push-ups and by removing all privacy. Prisoners rebelled by throwing pillows and trashing their cells. Some prisoners became so immersed in their roles that they exhibited symptoms of mental breakdown; however, according to Zimbardo, none of the participants suffered long term harm (Alexander, 2001).

This text is adapted from OpenStax, Psychology. OpenStax CNX.

Suggested Reading

Haslam, S. A., Reicher, S., & Van Bavel, J. J. (2018, June 27). Rethinking the nature of cruelty: The role of identity leadership in the Stanford Prison Experiment. https://doi.org/10.31234/osf.io/b7crx

Alexander, M. (2001, August 22). Thirty years later, Stanford prison experiment lives on.  Stanford Report . Retrieved from http://news.stanford.edu/news/2001/august22/prison2-822.html.

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How the Stanford Prison Experiment Worked

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An Infamous Experiment

The Stanford Prison Experiment is so well-known that even people who've never taken a course in psychology have heard of it, and anyone who does study psychology learns about it in introductory courses. The events of the experiment are told and retold among social scientists and people interested in human behavior like a spooky campfire story.

Philip Zimbardo carried out the experiment, which was funded by the U.S. Office of Naval Research, in August 1971 at Stanford University. The applicants took psychological tests to ensure they were "average," or didn't have psychological disorders or medical conditions. The researchers recruited two dozen male college students using advertisements in newspapers, paying them $15 per day to spend two weeks in a mock prison. They were randomly divided into groups identified as either guards or prisoners, and the prisoners were "arrested" at their homes without warning by real cops and booked at the Palo Alto police station before being taken to the mock prison. The guards weren't instructed how to do their jobs, but they did create a list of restrictive rules the prisoners had to follow, including remaining silent during rest periods and not using each other's names. Zimbardo (acting as prison superintendent) and a team of researchers (one of whom acted as warden) observed the experiment.

The results were horrifying. The guards adopted a rapidly escalating pattern of humiliation and dehumanization against the prisoners. They turned the prisoners against each other and imposed increasingly bizarre punishments, held in check only by the researchers' rule that no physical violence was allowed. Five prisoners were released early because they suffered serious emotional breakdowns or physical problems [source: Zimbardo ]. The other prisoners meekly submitted to whatever treatment the guards dished out and eagerly turned against one another at the prospect of a reward, such as being allowed to sleep in a cell with beds and blankets instead of on the concrete floor. The participants became so invested in their roles that the entire experiment was halted after just six days, when Zimbardo realized it was spiraling out of control.

The lesson of the Stanford Prison Experiment seems pretty obvious: There's a cruel streak inside all people, a latent evil waiting to be unleashed should they be given the slightest hint of authority and power. By the same token, the results of the experiment could show that people are driven to obey, conform and respond to authority with submission and compliance. It's a profound and disquieting statement about human nature that 24 "average" young men could be so easily and quickly twisted.

But things aren't really so simple. The lessons to be learned aren't confined to "guards" and "prisoners," but extend to prisons and other powerful institutions, and even to the ways scientists conduct experiments on human behavior. What really happened at the "Stanford County Prison"? Let's find out.

In interviews, Zimbardo often describes the process of dividing the participants into guards and prisoners as a coin flip. This deserves some clarification. Randomization , a method of sampling in experiments, is determined using a computer program of some kind (even in 1971), because often complex factors need to be accounted for to control variables. An actual coin flip couldn't be used even in the Stanford Prison Experiment, because you might not get 24 heads and 24 tails in 48 flips. The odds of an individual participant getting placed in one group or the other were indeed 50-50, like a coin flip, but the researchers didn't actually flip a coin.

Please copy/paste the following text to properly cite this HowStuffWorks.com article:

The Stanford Prison Experiment is based on lies. Hear them for yourself.

This damning audio debunks the famed research.

by Brian Resnick

The Stanford Prison Experiment — one of the most infamous psychological spectacles of all time — was purported to show how circumstances can bring out the worst in all of us. In the experiment, 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. It was supposed to be a naturalistic exercise on what happens when some people are given power and others are denied it.

Critically, Zimbardo stated in a 1971 document describing the experiment that “the guards were given no specific instruction or training on how to be guards.”

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

“Instead,” he said, “they were free, within limits, to do whatever they thought was necessary to maintain law and order in the prison and to command the respect of the prisoner.”

This week, the story of the experiment changed considerably. In a thoroughly reported exposé on Medium, journalist Ben Blum finds compelling evidence that the guards in this experiment were not left to act on their own desires. Audio recording and interviews with those involved reveal the guards were coached into being mean or considered the experiment to be an “improv exercise.” Here is one of those recordings, via the Stanford archive . It’s pretty damning. You can hear David Jaffe, one of Zimbardo’s students who acted as the prison “warden,” chastising a guard for not being severe enough.

(The quality of the audio is not great. It is, after all, a nearly 50-year-old tape cassette recording. You can read the transcript below. Emphasis added.)

JAFFE: Generally, you’ve been kind of in the background. Part of that is my fault because I’ve gone along with when you wanted to sit outside while they were doing count. Or that sort of thing. But we really want to get you active and involved. Because the guards have to know that every guard is going to be what we call a “tough guard.” And so far ... GUARD: I’m not too tough. JAFFE: Yeah. Well, you have to try to get it in you. GUARD: Well, I don’t know about that. JAFFE: See, the thing is, what I mean by tough is you have to be firm, and you have to be in the action, and that sort of thing. It’s really important for the workings of the experiment because whether or not we can make this thing seem like a prison, which is the aim of the thing depends largely on the guards’ behavior.

These revelations significantly change the conclusions of the experiment, if you can even call it that anymore. (Many now think of it as much more of a dramatic demonstration than a serious scientific endeavor. And recall: It was even terminated before its set end date.) That some of the guards were coached cuts against the implication that being placed in a position of power leads to cruelty. If anything, it shows how an authority figure can persuade another into conformity.

“The bottom line is that conformity isn’t natural, blind or inevitable,” NYU social psychologist Jay Van Bavel tweeted in light of these revelations. “Zimbardo was not only deeply wrong about this — but his public comments misled millions of people into accepting this false narrative about the Stanford Prison Experiment.”

Further reading: the prison experiment

• Ben Blum’s piece on Medium is a great piece of reporting. Read it here .
• What’s with all these famous psychology experiments coming under fire recently? I explain how the prison experiment fits into the field’s larger “replication crisis.”

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Stanford Prison Experiment

• Quiet Rage: The Stanford Prison Experiment

Prisoner Rules Prepared by the Warden and Guards

Bibliography.

the InMind blog

Bug or feature boredom feels aversive, and this is why it matters.

written by Wanja Wolff, Katja Rewitz & Dr. Maik Bieleke

Doing ill for ‘the greater good’: Understanding what really went on in the Stanford Prison Experiment

• written by Alex Haslam , Stephen Reicher & Jay Van Bavel

Just about every highschool and college psychology textbook offers extensive coverage of Zimbardo’s Stanford Prison Experiment (SPE). The meaning of the SPE seemed obvious — that when given roles with power , people naturally become brutal tyrants. This message has had lasting influence, not only in psychology but in the world at large. However, after researchers have recently gained access to the SPE archives, it has come to light that much of what we thought we knew about the study is inaccurate. We asked three experts to weigh in on these recent events, and the resulting discussion is one that offers valuable insights not only into the SPE but also into the role of debate in science and way that we engage with, and teach about, psychology’s classic studies.   

Few readers will be unfamiliar with the story of the Stanford Prison Experiment (SPE). Conducted in the summer of 1971, the study involved randomly assigning 18 college students to roles as Prisoners and Guards in a simulated prison that had been created in the basement of the Department of Psychology at Stanford University [ 1 , 2 ]. The researchers’ claim was that they simply stood back and watched what happened, and, in particular, that they provided no training to the Guards.

Their hypothesis was that the participants’ “behavioural scripts associated with the oppositional roles of Prisoner and Guard” — which were “the sole source of guidance” — would be sufficient for the prison to turn nasty [ 3 ]. There is little question that things did indeed turned nasty: after just six days the study had to be abandoned out of fear for the Prisoners’ welfare, such was the brutality of the Guards.

In the intervening 47 years this is a story that has been told by Zimbardo again and again, in media interviews, public lectures, and on the official website for the study. It was also a story that he retold in 2003 as he contributed to the legal defence of those who abused detainees at Abu Ghraib prison in Iraq. Here Zimbardo argued that the brutal acts that shocked the world were evidence of the power of roles to subvert perpetrators’ character and morality. He labelled this “The Lucifer Effect” — the title of his best-selling 2007 book [ 4 ] which also provided the basis for Kyle Alavarez’s eponymous film which faithfully and dramatically reenacted Zimbardo’s official version of events in the SPE [ 5 ]. This story is a staple of most of introductory psychology textbooks [ 6 ] and is retold to tens of thousands of college and high school students around the world every year [ 7 ].

In recent weeks, however, there has been another surge of interest in the SPE, rivalling any that have gone before. This time, though, the story is very different. It coincides with the digitization of material from the SPE in the Stanford University archives [ 8 ] which, for the first time, gives researchers (and anyone else who is interested) direct access to evidence from the study itself. In particular, it reveals hitherto unknown information about how Zimbardo and his colleagues conducted their research. Since the original paper was not published in a traditional peer-reviewed psychology journal, these critical methodological details have been hidden to scholars—and the public—for the past half century.

There is a wealth of such material in the archive, and researchers are now beginning to pore over it with interest. In this they have been guided by the exhaustive forensic work of the French researcher Thibault Le Texier [ 9 ], closely (and independently) followed by American journalist Ben Blum [ 10 ]. The title of Le Texier’s book —  Histoire D’Un Mensonge  [ Story of a Lie ] — gives a clear indication of his findings. Blum also uses the same word,  lie , to sum up his conclusion. The bottom line for both researchers is that many of the things we thought we knew about the SPE are flatly contradicted by the newly unearthed evidence.

Perhaps the most revealing piece of evidence in the archive is an 18-minute tape recording of a meeting between Zimbardo’s prison Warden, David Jaffe, and a reluctant Guard, John Mark [ 11 ]. This recording can be accessed at  https://purl.stanford.edu/wn708sg0050  (from 8:38 onwards).  Before you read on, we strongly recommend that you listen to this recording with your own ears and ask yourself: Is the guard conforming blindly to his role as a brutal guard or is he being pressured by the Warden to behave this way?

What you can hear on the tape is a Warden repeatedly cajoling the Guard to “toughen up”. He starts by saying “ We noticed this morning that you weren’t really lending a hand … but we really want to get you active and involved because the Guards have to know that every Guard is going to be what we call a tough Guard” . The Guard, John Mark, repeatedly resists this pressure from the Warden over the course of the meeting. Eventually, the Warden declares: “ When there’s a situation … [you have]  to have to go in there and shout if necessary. To be more  into  the action. ”

Far from being left to their own devices, it is thus clear that the Guards—or at least this one Guard—were told what they had to do, and then asked to account for themselves if they didn’t. It is not clear how many guards were exposed to pressure of this form, but it seems likely that even if only one Guard was told to behave this way, the message would have been shared among the Guards as the study progressed (noting that this was instruction directed at “every Guard”).  

This evidence blows Zimbardo’s role account out of the water. For what one sees in the meeting is that the Warden characterizes the Guard not as a research participant but as a confederate who is expected to act in ways defined by the Experimenters. Unsurprisingly, perhaps, no mention was made of such meetings in Zimbardo’s 2007 book, and they are conspicuously absent from Alvarez’s movie. While an early paper did allude to the fact that the Guards thought the Experimenters were primarily interested in the Prisoners’ behaviour [1, p.75], the significance of this point was never elaborated upon, and it was then dropped from later accounts.

This type of instruction is unheard of in psychology experiments. Indeed, Experimenters are expected to take steps to ensure that their actions, even subtle ones, do not unduly influence the behaviour of participants. But in this case, the Experimenters’ influence attempts were anything but subtle. In the face ongoing and stubborn resistance from the participant they took the form of explicit, repeated instructions to engage in patterns of behaviour that supported Zimbardo’s research goals.

Almost everyone we have shared this recording with has concluded that Zimbardo’s account of the SPE actually is deeply flawed. To ensure these intuitions had some validity, we conducted a Twitter poll asking people to listen to the tape and then evaluate Zimbardo’s account. This, of course, is not a scientific test. Nevertheless, just 4% of respondents felt that what happened in the meeting between Warden Jaffe and Guard Mark was consistent with the idea that the Guards in the SPE conformed “naturally” to role (the phrase used in the original article on the study [ 12 ]). In short, then, the received story about the Stanford Prison Experiment simply does not hold up in the face of the new evidence.

Although we were surprised to find such convincing evidence (evidence that, to be frank, we would have struggled to make up), its content was not wholly surprising to us. There had always been rumours that the SPE was not all that it seemed. Amongst other things, a number of letters published in the  Stanford Daily  over the years had suggested that the Experimenters had been more interventionist than they admitted. Thus, in 2007 the resistant Guard, John Mark, wrote that: “My opinion, based on my observations, was that Zimbardo began with a preformed blockbuster conclusion and designed an experiment to ‘prove’ that conclusion” [ 13 ].

Even before this, in 2006, we had noted that snippets of information that were already in the public  domain  — such as Zimbardo’s original briefing to his Guards which forms part of his film ‘Quiet Rage’ [ 14 ]  —   pointed to the importance of the Experimenter’s leadership in producing the toxicity of the SPE. But such evidence was limited in quantity and quality. It was hardly enough to topple what is possibly the single most famous study in social psychology. But the news from the archive and the Jaffe-Mark tape completely transform our understanding of this classic study. Now the evidence of the Experimenters’ intervention and leadership is simply undeniable.

Faced with this new evidence, one response has been to urge psychologists to wash their hands of the SPE. Tellingly, both Le Texier and Blum press for the study to be labelled as fraudulent and purged from classrooms and textbooks. We understand this response. Whether it will be successful is a quite different question. As Richard Griggs has noted [10], in the past, textbook authors have been reluctant to discuss the SPE’s shortcomings in favour of a simple compelling story.

But this new evidence is of a qualitatively different order. Moreover, it comes in the midst of greatly heightened concern about scientific fraud and misconduct. Certainly, it would be better to have the study expunged from the scientific record than to perpetuate a story which is strikingly inconsistent with the facts.

At the same time, we would urge against so sweeping a response. Certainly, the SPE is deeply flawed. The accounts we have been given omit crucial information, the degree of guard brutality is overemphasised, and Zimbardo’s explanation of the study is plainly untenable.

But it remains undeniable that  some  Guards did act in extreme ways.  So we still accept Zimbardo’s claim that the SPE is a powerful demonstration of the capacity for ordinary men to be turned to evil. But this needs to be properly explained. In this respect, at the same time as it discredits the old analysis, the information that has emerged from the archive is extremely helpful.

We were always concerned with what we saw as excessive interventionism with the SPE. That is why, when two of us ran our own prison study [ 15 ] we consciously declined to tell our participants what to do. In the absence of such direction, our Guards were very unwilling to take on their role and to impose discipline. This meant that they became increasingly unable to keep the Prisoners in order and eventually the system collapsed. It was only when a leader who promised to restore law and order in the prison came to the fore and cultivated a following among new Guards that the spectre of oppression akin to that seen in the SPE surfaced.

Over time, that experience motivated us to examine the role of leadership in toxic behaviour more generally, looking both at other studies that address how ordinary people can act with inhumanity (notably Milgram’s Obedience to Authority studies [ 16 ]) and real-world examples such as the Holocaust and the Rwandan genocide [ 17 , 18 ]. This work culminated in a model of ‘identity leadership’ which argues that brutality occurs to the extent that leaders are able to persuade people (1) that they are part of a common group, (2) that the group’s cause is worthy, and (3) that brutal acts are necessary for the achievement of group goals [ 19 , 20 ].

But although the SPE set us on the path towards an identity leadership analysis, we were unable to find clear evidence that such an analysis could explain what happened in the SPE. Until now. As we show in a paper we have just submitted for publication [ 21 ], the archives provide us with the critical evidence to complete our argument.

What we hear in Warden Jaffe’s cajoling of Guard Mark is precisely the hallmarks of identity leadership. First, the Warden repeatedly uses collective pronouns (“we”) to characterize their relationship, endeavoring to position the Experimenters and Guards as a team working toward a common goal . Second, Warden Jaffe does not tell Mark to be tough for its own sake. Rather he tries to persuade him that toughness is something  necessary  for the achievement of shared ingroup goals. And, third he presents that cause as one that is fundamentally  noble and worth y.

In this case, the cause was much-needed improvement to the U.S. correctional system.  “ Hopefully what will come out of this study”,  the Warden tells the Guard , “is some very serious recommendations for reform, at least reform, if not, you know, revolutionary-type reform”.  “We’re not doing this because we’re sadists” , he says, we’re doing it to make the world a better place. This, then, is the very essence of identity leadership.

The end of tyranny

For the past 10 years we have sought to engage Zimbardo in debate around the above ideas. Not least, we have done so through peer-reviewed publications in leading journals that address the broad range of issues that his and our work raises — those concerning not only the origins of tyranny and resistance [ 22 ], but also the nature of leadership and followership [ 23 , 24 ], and the social determinants of stress and mental health [ 25 ]. 

These efforts have failed. Zimbardo has responded by labelling our prison study ‘reality TV’ [ 26 ], as deplorable, shameful and fraudulent [ 27 , 28 ], and he describes us as mere ‘bloggers’ [ 29 ]. What is fascinating here is the way that Zimbardo — responding to us and his other critics — uses the very same rhetorical techniques to try and engage the audience on his side as his Warden, Jaffe, used to try and engage Mark in the SPE. That is, he insists that his work is a moral crusade, aimed at promoting social justice. And that therefore those who threaten to derail his position need to be swatted aside for the sake of the cause.

As Zimbardo himself is unwilling to reconsider the meaning of his study, then we ask you, the reader, to listen to the evidence with your own ears and tell us what you hear. If you share our concern that his story does not fit his data, then we encourage you to change how you talk about the SPE to your students, colleagues and members of the public at large.

Correspondence regarding this piece can be addressed to Alex Haslam, School of Psychology, University of Queensland, St. Lucia QLD 4072, Australia; e-mail: [email protected] ; Tel.: +61 (0)7 3346 9157

[1] Haney, C., Banks, C. & Zimbardo, P. (1973). A study of prisoners and guards in a simulated prison.  Naval Research Reviews . September (pp.1-17). Office of Naval Research: Washington, D.C.

[2] Haney, C., Banks, C., & Zimbardo, P. G. (1973). Interpersonal dynamics in a simulated prison.  International Journal of Criminology and Penology ,  1 , 69–97.

[3] Zimbardo, P. G. (2004). A situationist perspective on the psychology of evil: Understanding how good people are transformed into perpetrators. In A.Miller (Ed.),  The social psychology of good and evil  (pp.21–50).New York: Guilford. (p.39)

[4] Zimbardo, P. (2007).  The Lucifer Effect: How good people turn evil. London: Random House.

[5] Alvarez, K. P. (Dir.) (2015).  The Stanford Prison Experiment [Motion picture]. New York: IFC Films.

[6] Griggs, R. A. (2014). Coverage of the Stanford Prison Experiment in introductory psychology textbooks.  Teaching of Psychology ,  41 , 195-203.

[7] Bartels, J. M., Milovich, M. M., & Moussier, S. (2016). Coverage of the Stanford prison experiment in introductory psychology courses: A survey of introductory psychology instructors.  Teaching of Psychology ,  43 , 136-141.

[8] https://searchworks.stanford.edu/catalog?f%5Bcollection%5D%5B%5D=6022627

[9] Le Texier, T. (2018).  Histoire d’un mensonge: Enquête sur l’experience de Stanford . Editions la Découverte: Paris. 

[10] Blum, B. (2018). The lifespan of a lie.  Medium . https://medium.com/s/trustissues/the-lifespan-of-a-lie-d869212b1f62

[11] Accessible at:  http://purl.stanford.edu/wn708sg0050

[12] Haney, C., Banks, C. & Zimbardo, P. (1973). A study of prisoners and guards in a simulated prison.  Naval Research Reviews . September (pp.1-17). Office of Naval Research: Washington, D.C. (p.12)

[13] See: https://alumni.stanford.edu/get/page/magazine/article/?article_id=32561

[14] Zimbardo, P. (1989). Quiet rage  (video). Stanford, CA: Stanford University.

[15] Reicher, S. D., & Haslam, S. A. (2006). Rethinking the psychology of tyranny: The BBC Prison Experiment.  British Journal of Social Psychology ,  45 , 1-40.

[16] Milgram, S. (1974).  Obedience to authority: An experimental view.  New York: Harper & Row.

[17] Haslam, S. A., & Reicher, S. D. (2012). Contesting the “nature” of conformity: What Milgram and Zimbardo’s studies really show.  PLoS Biology ,  10 (11): e1001426.

[18] Reicher, S., Haslam, S. A., & Rath, R. (2008). Making a virtue of evil: A five‐step social identity model of the development of collective hate.  Social and Personality Psychology Compass ,  2 (3), 1313-1344.

[19] Haslam, S. A., & Reicher, S. D. (2007). Beyond the banality of evil: Three dynamics of an interactionist social psychology of tyranny.  Personality and Social Psychology Bulletin, 33 , 615-622.

[20] Haslam, S. A., & Reicher, S. D. (2017). 50 years of “obedience to authority”: From blind obedience to engaged followership.  Annual Review of Law and Social Science ,  13 , 59-78. e109015. doi:10.1146/annurev-lawsocsci-110316-113710

[21] Haslam, S. A., Reicher, S. D., Ranz-Schleifer, N., & Van Bavel. (2018).Rethinking the ‘nature’ of brutality: Uncovering the role of identity leadership in the Stanford Prison Experiment. Accessible at PsyArXiv Preprints: https://psyarxiv.com/b7crx

[22] Haslam, S. A., & Reicher, S. D. (2012a). When prisoners take over the prison: A social psychology of resistance.  Personality and Social Psychology Review ,  16 , 154-179.

[23] Reicher, S. D., Haslam, S. A., & Hopkins, N. (2005). Social identity and the dynamics of leadership: Leaders and followers as collaborative agents in the transformation of social reality.  Leadership Quarterly, 16 , 547-568.

[24] Haslam, S. A., & Reicher, S. D. (2007). Identity entrepreneurship and the consequences of identity failure: The dynamics of leadership in the BBC Prison Study.  Social Psychology Quarterly , 70 , 125-147. doi:10.1177/019027250707000204

[25] Haslam, S. A., & Reicher, S. D. (2006). Stressing the group: Social identity and the unfolding dynamics of responses to stress.  Journal of Applied Psychology, 91 , 1037-1052. doi:10.1037/0021-9010.91.5.1037

[26] See: http://www.prisonexp.org/response

[27] See: https://twitter.com/alexanderhaslam/status/1011876643927883776

[28] Zimbardo, P. (2006). On rethinking the psychology of tyranny: The BBC Prison Study.  British Journal of Social Psychology ,  45 , 47–53.

[29] See: https://www.vox.com/science-and-health/2018/6/28/17509470/stanford-priso...

article author(s)

Alex Haslam

Alex Haslam is Professor of Psychology and Australian Laureate Fellow at the University of Queensland. His research focuses on the study of group and... more

Stephen Reicher

Stephen Reicher is Wardlaw Professor of Psychology at the University of St. Andrews. His research is on social identity and group processes. Stephen is a... more

Jay Van Bavel

Jay Van Bavel is an Associate Professor of Psychology & Neural Science at New York University, an affiliate at the Stern School of Business in... more

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The Stanford Prison Experiment

In 1971, twenty-four male students are selected to take on randomly assigned roles of prisoners and guards in a mock prison situated in the basement of the Stanford psychology building. In 1971, twenty-four male students are selected to take on randomly assigned roles of prisoners and guards in a mock prison situated in the basement of the Stanford psychology building. In 1971, twenty-four male students are selected to take on randomly assigned roles of prisoners and guards in a mock prison situated in the basement of the Stanford psychology building.

• Kyle Patrick Alvarez
• Tim Talbott
• Philip Zimbardo
• Ezra Miller
• Tye Sheridan
• Billy Crudup
• 130 User reviews
• 91 Critic reviews
• 67 Metascore
• 4 wins & 3 nominations

Top cast 38

• Daniel Culp …

• Peter Mitchell …

• Dr. Philip Zimbardo

• Dr. Christina Maslach

• Christopher Archer

• Anthony Carroll

• John Lovett

• Gavin Lee …

• Prisoner 416

• Jerry Sherman …

• Jeff Jansen …

• Jesse Fletcher

• Kyle Parker

• Paul Beattie …

• Hubbie Whitlow …
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Did you know

• Trivia Although never mentioned in the movie, the real life experiment was funded by the U.S. Office of Naval Research and was of interest to both the U.S. Navy and Marine Corps as an investigation into the causes of conflict between military guards and prisoners.
• Goofs When Dr. Zimbardo speaks with his colleague, the colleague says that he will see him at the beginning of the semester. Stanford does not have semesters; rather, it has a quarter academic calendar.

Daniel Culp : I know you're a nice guy.

Christopher Archer : So why do you hate me?

Daniel Culp : Because I know what you can become.

• Connections Featured in WatchMojo: Top 10 Creepiest Historic Events That Are Scarier than Horror Movies (2020)

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• palavitsinis
• Nov 23, 2015
• How long is The Stanford Prison Experiment? Powered by Alexa
• July 17, 2015 (United States)
• United States
• Official site
• Untitled Stanford Prison Experiment Project
• Stanford University, Palo Alto, California, USA
• Coup d'Etat Films
• Sandbar Pictures
• Abandon Pictures
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• Jul 19, 2015

Technical specs

• Runtime 2 hours 2 minutes

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