stanford prison experiment key findings

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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IResearchNet

Stanford Prison Experiment

The Stanford Prison Experiment (SPE) is a highly influential and controversial study run by Philip Zimbardo and his colleagues at Stanford University in 1971. The researchers originally set out to support the notion that situational forces are just as powerful and perhaps more powerful than dispositional forces in influencing prison behavior. In addition to providing support for their hypothesis, the study was heavily covered in the mainstream media and had far-reaching ethical implications. Regardless, and perhaps because of its controversial nature, the SPE remains one of the most well-known experiments in social psychology.

The Purpose of the Stanford Prison Experiment

Stanford Prison Experiment Methodology

To test their hypothesis, Zimbardo and colleagues created a realistic mock prison in the basement of Stanford University. The participants included 21 male college students, specifically chosen for their normal responses on a battery of background questionnaires. The participants were randomly assigned to be either a guard or a prisoner, with an undergraduate research assistant acting as warden and Zimbardo himself taking on the role of superintendent. The prisoners stayed in the prison 24 hours per day, while the guards worked 8-hour shifts. Aside from a restriction on physical violence, guards were given great latitude in how they could deal with prisoners, including the rules they could establish and punishments they could dole out.

The experimenters went to great lengths to establish realism. Prisoners were unexpectedly “arrested” at their houses by the local police department, were taken to the police station to be charged their “crime” and brought to the prison at Stanford. Prisoners were assigned a number and wore only a smock, which was designed to deindividuate the prisoners. Guards were fitted with a uniform, nightstick, and reflective sunglasses to establish power. The prison cells consisted of a 6- by 9-foot space furnished with only a cot. To further increase realism, a catholic priest and attorney were brought in and a parole board was established.

Once the participants had arrived at the prison, the situation escalated at a surprising rate. On the second day, a prisoner rebellion was quickly quelled by the guards, who punished the prisoners through means conceived without guidance from the experimenters. For example, prisoners were stripped naked, forced to do menial tasks, and in many cases were deprived of their cots, meals, and bathroom privileges. After the attempted revolt and subsequent punishment, five prisoners began to experience extreme emotional reactions and were eventually released. As the obedience tactics became more brutal and humiliating and prisoners displayed increasingly negative affectivity, Zimbardo eventually decided to end the study on the sixth day of what had been planned as a 2-week study.

Findings of the Stanford Prison Experiment

Zimbardo and colleagues construed the increasingly hostile behavior of the guards and increasingly passive behavior of the prisoners, each of which had started out as groups of normal young men, as evidence that the extreme nature of the prison situation breeds such volatile and desperate behavior. Indeed, the SPE is often cited as evidence for the strong role of the situation over individuals in ways in which they often do not predict. The researchers also compared their work to Stanley Milgram’s research on obedience in that both provide support for the notion that given an extreme situation, good people can be coerced into doing evil things. Despite these exciting findings, the SPE has been criticized from both a methodological and ethical standpoint.

Methodological Criticisms of the Stanford Prison Experiment

Methodologically, critics have argued that participants of the SPE never fully accepted the situation as real and were merely playing the stereotypic roles of prisoners and guards. In essence, it was argued that the results were driven by demand characteristics of the experimental situation. It did not help the original authors’ argument that Zimbardo himself played a prominent role in the experiment, sometimes guiding the way in which the study played out. Regardless, evidence suggests that participants did internalize the situation, as well as their roles in the situation. For instance, only one-tenth of the conversations between prisoners contained speech about life outside of the experiment.

Ethical Criticisms of the Stanford Prison Experiment

The SPE was likely more controversial from an ethical point of view. The ethical implications of the study, as well as Zimbardo’s dual role as investigator and superintendent of the Stanford prison were highly criticized at the time. Zimbardo himself admitted that his own acceptance of the prison situation and his desire to run a good prison clouded his judgment, suggesting that even he had internalized his role in the situation. Although the experiment did conform to the guidelines set forth by the ethics review board at the time, few would argue that the sadistic and humiliating acts performed during the study were ethical by today’s standards. Even Zimbardo admits that it was unethical for the study to continue after the first prisoner showed an extreme negative reaction.

Stanford Prison Experiment Replications

Stephen Reicher and S. Alexander Haslam attempted to replicate the SPE, skirting ethical guidelines through allowing the experiment to take place in the context of a British reality television show. The results of the SPE were not replicated; in Reicher and Haslam’s version, the guards never organized themselves and were eventually overthrown.

References:

• Adam, D. (2002). Reality TV show recreates famed social study. Nature, 417, 213.
• Haney, C., Banks, C., & Zimbardo, P. (1973). Interpersonal dynamics in a simulated prison. International Journal of Criminology and Penology, 1, 69-97.
• Zimbardo, P. G., Maslach, C., & Haney, C. (1999). Reflections on the Stanford Prison Experiment: Genesis, transformations, consequences. In T. Blass (Ed.), Obedience to authority: Current perspectives on the Milgram paradigm (pp. 193-237). Mahwah, NJ: Erlbaum.

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The Stanford Prison Experiment

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

Cara Lustik is a fact-checker and copywriter.

• 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.

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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."

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

• 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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What the Stanford Prison Experiment Taught Us

In August of 1971, Dr. Philip G. Zimbardo of Stanford University in California conducted what is widely considered one of the most influential experiments in social psychology to date. Made into a New York Times best seller in 2007 ( The Lucifer Effect ) and a major motion picture in 2015 ( The Stanford Prison Experiment ), the Stanford Prison Experiment has integrated itself not only into the psychology community but also popular culture. The events that occurred within this experiment, though disturbing, have given many people insight into just how much a situation can affect behavior. They have also caused many to ponder the nature of evil. How disturbing was it? Well, the proposed two-week experiment was terminated after just six days, due to alarming levels of mistreatment and brutality perpetrated on student “prisoners” by fellow student “guards.”

The study aimed to test the effects of prison life on behavior and wanted to tackle the effects of situational behavior rather than just those of disposition. After placing an ad in the newspaper, Zimbardo selected 24 mentally and physically healthy undergraduate students to participate in the study. The idea was to randomly assign nine boys to be prisoners, nine to be guards, and six to be extras should they need to make any replacements. After randomly assigning the boys, the nine deemed prisoners were “arrested” and promptly brought into a makeshift Stanford County Prison, which was really just the basement of the Stanford Psychology Department building. Upon arrival, the boys’ heads were shaved, and they were subjected to a strip search as well as delousing (measures taken to dehumanize the prisoners). Each prisoner was then issued a uniform and a number to increase anonymity. The guards who were to be in charge of the prisoners were not given any formal training; they were to make up their own set of rules as to how they would govern their prison.

Over the course of six days, a shocking set of events unfolded. While day one seemed to go by without issue, on the second day there was a rebellion, causing guards to spray prisoners with a fire extinguisher in order to force them further into their cells. The guards took the prisoners’ beds and even utilized solitary confinement. They also began to use psychological tactics, attempting to break prisoner solidarity by creating a privilege cell. With each member of the experiment, including Zimbardo, falling deeper into their roles, this “prison” life quickly became a real and threatening situation for many. Thirty-six hours into the experiment, prisoner #8612 was released on account of acute emotional distress, but only after (incorrectly) telling his prison-mates that they were trapped and not allowed to leave, insisting that it was no longer an experiment. This perpetuated a lot of the fears that many of the prisoners were already experiencing, which caused prisoner #819 to be released a day later after becoming hysterical in Dr. Zimbardo’s office.

The guards got even crueler and more unusual in their punishments as time progressed, forcing prisoners to participate in sexual situations such as leap-frogging each other’s partially naked bodies. They took food privileges away and forced the prisoners to insult one another. Even the prisoners fell victim to their roles of submission. At a fake parole board hearing, each of them was asked if they would forfeit all money earned should they be allowed to leave the prison immediately. Most of them said yes, then were upset when they were not granted parole, despite the fact that they were allowed to opt out of the experiment at any time. They had fallen too far into submissive roles to remember, or even consider, their rights.

On the sixth day, Dr. Zimbardo closed the experiment due to the continuing degradation of the prisoners’ emotional and mental states. While his findings were, at times, a terrifying glimpse into the capabilities of humanity, they also advanced the understanding of the psychological community. When it came to the torture done at Abu Ghraib or the Rape of Nanjing in China, Zimbardo’s findings allowed for psychologists to understand evil behavior as a situational occurrence and not always a dispositional one.

Learn More About This Topic

• How does a situation cause violent behavior?
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Know a mentally disturbed person who doesn’t think much of others? Make sure you apply the right epithet.

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• Visit the Stanford Prison Experiment official website

The Stanford Prison Experiment: The Power of the Situation

• First Online: 20 January 2024

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

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

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

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

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Zimbardo, P. G. (1970). The human choice: Individuation, reason, and order versus deindividuation, impulse, and chaos. In W. J. Arnold & D. Levine (Eds.), 1969 Nebraska symposium on motivation (pp. 237–307). University of Nebraska Press. Accessed January 19, 2022, from https://stacks.stanford.edu/file/gk002bt7757/gk002bt7757.pdf

Zimbardo, P. G. (1971a). Application for institutional approval of research involving human subjects . August, 1971. Available at: http://www.prisonexp.org/pdf/humansubjects.pdf . Accessed December 1, 2023.

Zimbardo, P. G. (1971b). Prison life study: General information sheet . August, 1971. Available at: http://www.prisonexp.org/pdf/geninfo.pdf . Accessed December 1, 2023.

Zimbardo, P. G. (2008). The lucifer effect: Understanding how good people turn evil . Random House.

Zimbardo, P. G., Haney, C., Banks, W. C., & Jaffe, D. (1972). Stanford prison experiment . Philip G. Zimbardo, Inc. (Tape recording).

Zimbardo, P. G., Haney, C., Banks, W. C., & Jaffe, D. (1972, April 8). The mind is a formidable jailer: A Pirandellian prison. New York Times Magazine, Section 6, 36, ff.

Zimbardo, P. G., Marshall, G., & Maslach, C. (1971). Liberating behavior from time-bound control: Expanding the present through hypnosis. Journal of Applied Social Psychology, 1 (4), 305–323. https://doi.org/10.1111/j.1559-1816.1971.tb00369.x

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Zimbardo, P. G., Maslach, C., & Haney, C. (2000). Chapter 11: Reflections on the Stanford prison experiment: Genesis, transformations, consequences. In T. Blass (Ed.), Obedience to authority: Current perspectives on the milgram paradigm (pp. 193–237). Lawrence Erlbaum Associates.

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

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

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Stanford Prison Experiment

• Quiet Rage: The Stanford Prison Experiment

About the Stanford Prison Experiment

Carried out August 15-21, 1971 in the basement of Jordan Hall, the Stanford Prison Experiment set out to examine the psychological effects of authority and powerlessness in a prison environment. The study, led by psychology professor Philip G. Zimbardo, recruited Stanford students using a local newspaper ad. Twenty-four students were carefully screened and randomly assigned into groups of prisoners and guards. The experiment, which was scheduled to last 1-2 weeks, ultimately had to be terminated on only the 6th day as the experiment escalated out of hand when the prisoners were forced to endure cruel and dehumanizing abuse at the hands of their peers. The experiment showed, in Dr. Zimbardo’s words, how “ordinary college students could do terrible things.”

This exhibit includes documentation of the experiment, including images and audiovisual recordings, that some viewers may find disturbing. Viewer discretion is advised.

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The Real Lesson of the Stanford Prison Experiment

By Maria Konnikova

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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Stanford Prison Experiment

In this post

In what is now commonly referred to as the ‘ Stanford Prison Experiment’ the researchers wanted to find out more about the psychology of prison life and if people who were given specific roles to play, would do so, according to what they believed that role should be.

The research has been deemed as one of the most controversial in history and its findings have been extremely influential in helping us to understand why people may conform to a role that is expected of them.

Although the details of the research are included below, the following link leads to an excellent and more comprehensive look at the study, which should help you better understand it: http://www.prisonexp.org/

The researchers wanted to find out how readily their participants would conform to the roles given to them (either prisoner or guard) in a simulated prison environment.

Zimbardo, in particular, was interested in seeing if alleged brutality among prison guards in the US was due to the personality of the guard or the prison environment in which they worked.

• The basement of Stanford University in California was turned into a mocked-up prison
• Adverts were placed asking for participants to take on a role within the prison, which they would be expected to carry out for two weeks
• Would-be applicants were subject to diagnostic interviews and personality tests to eliminate those who had psychological problems, medical disabilities, or a history of crime or drug abuse
• 24 male participants were chosen from 75 volunteers and each was paid $15 per day to take part
• Participants were randomly assigned to the role of either prisoner or guard, and after some dropped out the researchers were eventually left with 10 prisoners and 11 guards
• Guards worked in eight-hour shifts and prisoners were assigned in threes to their ‘cells’
• ‘Prisoners’ were ‘arrested’ at their homes at the start of the experiment and each was subjected to being fingerprinted and blindfolded before being driven to the ‘prison’
• Upon arrival the prisoners were stripped, given uniforms and all their personal belongings were taken from them. Each was, thereafter, only referred to by his ID number
• Guards wore identical uniforms and told to do whatever they thought necessary to retain order within the prison
• Zimbardo himself acted as a prison warder and observed the behaviour of the participants

Zimbardo and his colleagues were astonished by what they found. The behaviour of the guards was so brutal that despite wanting to run the experiment for two weeks, the researchers were forced to terminate it after just six days. They found the following:

• All participants settled into their roles very quickly
• Within hours, some guards began to harass the prisoners and appeared to enjoy taunting them
• Once the harassment began, other guards began to join in and their behaviour worsened very quickly
• The prisoners were quick to behave like prisoners – they ‘told tales’ on each other and their behaviour quickly became very submissive
• On day two of the experiment, the prisoners staged a form of revolt but this was quickly extinguished by the guards and many prisoners were put into solitary confinement
• One prisoner had to be released from the experiment after just 36 hours, such was the level of his emotional distress
• Zimbardo realised that his own involvement in the experiment means he may have missed how bad the situation had become but all researchers agreed the experiment must end after six days

The researchers concluded that people will readily and quickly conform to the role that is expected of them, particularly if these are heavily stereotyped, such as a prison guard.

Zimbardo also concluded that it was the situation that someone found themselves in, rather than their personal characteristics, which made them conform to a specific role.

Many of the guards said that they were surprised by their own behaviour and they did not realise that they were capable of behaving in such a way – those acting as prisoners said something similar about their behaviour as well.

Strengths of the study

• Many of the participants were heard discussing ‘prison life’ as though it were real, meaning that their behaviour was genuine
• After the findings of the study were published, the American prison system was changed in that younger offenders were no longer housed with older ones, due to the risk of violence that they faced
• The experiment also ensured that stricter ethical guidelines about research were put into place

Weaknesses of the study

• The sample is biased as it only represented American males and therefore cannot be generalised across a wider population
• Participants may have shown demand characteristics because many claimed afterwards that they had simply been acting
• Ethical issues: it was found that there was a lack of informed consent among some participants. Some underwent extreme psychological distress and were not protected from this by the researchers

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Conformity to Social Roles as Investigated by Zimbardo

Last updated 22 Mar 2021

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

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

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

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

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

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

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

Evaluation of Zimbardo

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

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

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

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

• Social roles
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Biography of Philip Zimbardo

The Legacy of His Famous "Stanford Prison Experiment"

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Philip G. Zimbardo, born March 23, 1933, is an influential social psychologist. He is best known for the influential—yet controversial—study known as the “Stanford Prison Experiment,” a study in which research participants were “prisoners” and “guards” in a mock prison. In addition to the Stanford Prison Experiment, Zimbardo has worked on a wide range of research topics and has written over 50 books and published over 300 articles . Currently, he is a professor emeritus at Stanford University and president of the Heroic Imagination Project, an organization aimed at increasing heroic behavior among everyday people.

Early Life and Education

Zimbardo was born in 1933 and grew up in the South Bronx in New York City. Zimbardo writes  that living in an impoverished neighborhood as a child influenced his interest in psychology: “My interest in understanding the dynamics of human aggression and violence stems from early personal experiences” of living in a rough, violent neighborhood. Zimbardo credits his teachers with helping to encourage his interest in school and motivating him to become successful. After graduating from high school, he attended Brooklyn College, where he graduated in 1954 with a triple major in psychology, anthropology, and sociology. He studied psychology in graduate school at Yale, where he earned his MA in 1955 and his PhD in 1959. After graduating, Zimbardo taught at Yale, New York University, and Columbia, before moving to Stanford in 1968.

The Stanford Prison Study

In 1971, Zimbardo conducted his most famous and controversial study—the Stanford Prison Experiment. In this study , college-age men participated in a mock prison. Some of the men were randomly chosen to be prisoners and even went through mock “arrests” at their homes by local police before being brought to the mock prison on the Stanford campus. The other participants were chosen to be prison guards. Zimbardo assigned himself the role of the superintendent of the prison.

Although the study was originally planned to last two weeks, it was ended early—after just six days—because events at the prison took an unexpected turn. The guards began to act in cruel, abusive ways towards prisoners and forced them to engage in degrading and humiliating behaviors. Prisoners in the study began to show signs of depression, and some even experienced nervous breakdowns. On the fifth day of the study, Zimbardo’s girlfriend at the time, psychologist Christina Maslach, visited the mock prison and was shocked by what she saw. Maslach (who is now Zimbardo’s wife) told him, “You know what, it's terrible what you're doing to those boys.” After seeing the events of the prison from an outside perspective, Zimbardo stopped the study.

The Prison Experiment’s Impact

Why did people behave the way they did in the prison experiment? What was it about the experiment that made the prison guards behave so differently from how they did in everyday life?

According to Zimbardo, the Stanford Prison Experiment speaks to the powerful way that social contexts can shape our actions and cause us to behave in ways that would have been unthinkable to us even a few short days before. Even Zimbardo himself found that his behavior changed when he took on the role of prison superintendent. Once he identified with his role, he found that he had trouble recognizing the abuses happening in his own prison: “I lost my sense of compassion,” he explains in an interview with Pacific Standard .

Zimbardo explains that the prison experiment offers a surprising and unsettling finding about human nature. Because our behaviors are partially determined by the systems and situations we find ourselves in, we are capable of behaving in unexpected and alarming ways in extreme situations. He explains that, although people like to think of their behaviors as relatively stable and predictable, we sometimes act in ways that surprise even ourselves . Writing about the prison experiment in The New Yorker , Maria Konnikova offers another possible explanation for the results: she suggests that the environment of the prison was a powerful situation, and that people often change their behavior to match what they think is expected of them in situations such as this. In other words, the prison experiment shows that our behavior can change drastically depending on the environment we find ourselves in.

Critiques of the Prison Experiment

Although the Stanford Prison Experiment has had a significant influence (it was even the inspiration for a film), some people have questioned the validity of the experiment. Instead of simply being an outside observer of the study, Zimbardo served as the prison superintendent and had one of his students serve as the prison warden. Zimbardo himself has admitted that he regrets being the prison superintendent and should have remained more objective.

In a 2018 article for Medium, writer Ben Blum argues that the study suffers from several key flaws. First, he reports that several of the prisoners claimed being unable to leave the study (Zimbardo denies this allegation). Second, he suggests that Zimbardo’s student David Jaffe (the prison warden) may have influenced the behavior of the guards by encouraging them to treat prisoners more harshly.

It’s been pointed out that the Stanford Prison Experiment demonstrates the importance of reviewing the ethics of each research project before the study goes forward, and for researchers to think carefully about the study methods that they use. However, despite the controversies, the Stanford Prison Experiment raises a fascinating question: how much does the social context influence our behavior?

Other Work by Zimbardo

After conducting the Stanford Prison Experiment, Zimbardo went on to conduct research on several other topics, such as how we think about time  and how people can overcome shyness . Zimbardo has also worked to share his research with audiences outside of academia. In 2007, he wrote The Lucifer Effect: Understanding How Good People Turn Evil , based on what he learned about human nature through his research in the Stanford Prison Experiment. In 2008, he wrote The Time Paradox: The New Psychology of Time That Will Change Your Life about his research on time perspectives. He has also hosted a series of educational videos titled Discovering Psychology.

After the humanitarian abuses at Abu Ghraib came to light, Zimbardo has also spoken about the causes of abuse in prisons. Zimbardo was an expert witness  for one of the guards at Abu Ghraib, and he explained that he believed the cause of events at the prison were systemic. In other words, he argues that, rather than being due to the behavior of a “few bad apples,” the abuses at Abu Ghraib occurred because of the system organizing the prison. In a 2008 TED talk , he explains why he believes the events occurred at Abu Ghraib: “If you give people power without oversight, it's a prescription for abuse.” Zimbardo has also spoken about the need for prison reform in order to prevent future abuses at prisons: for example, in a 2015 interview with Newsweek , he explained the importance of having better oversight of prison guards in order to prevent abuses from happening at prisons.

Recent Research: Understanding Heroes

One of Zimbardo’s most recent projects involves researching the psychology of heroism. Why is it that some people are willing to risk their own safety to help others, and how can we encourage more people to stand up to injustice? Although the prison experiment shows how situations can powerfully shape our behavior, Zimbardo’s current research suggests that challenging situations don’t always cause us to behave in antisocial ways. Based on his research on heroes, Zimbardo writes that difficult situations can sometimes actually cause people to act as heroes: “A key insight from research on heroism so far is that the very same situations that inflame the hostile imagination in some people, making them villains, can also instill the heroic imagination in other people, prompting them to perform heroic deeds.” 

Currently, Zimbardo is president of the Heroic Imagination Project, a program that works to study heroic behavior and train people in strategies to behave heroically. Recently, for example, he has studied the frequency of heroic behaviors and the factors that cause people to act heroically. Importantly, Zimbardo has found from this research that everyday people can behave in heroic ways. In other words, despite the results of the Stanford Prison Experiment, his research has shown that negative behavior isn’t inevitable—instead, we are also capable of using challenging experiences as an opportunity to behave in ways that help other people. Zimbardo writes, “Some people argue humans are born good or born bad; I think that’s nonsense. We are all born with this tremendous capacity to be anything.”

• Bekiempis, Victoria. “What Philip Zimbardo and the Stanford Prison Experiment Tell Us About the Abuse of Power.”  Newsweek, 4 Aug. 2015, www.newsweek.com/stanford-prison-experiment-age-justice-reform-359247 .
• Blum, Ben. “ The Lifespan of a Lie. ” Medium: Trust Issues .
• Kilkenny, Katie. “‘It’s Painful’: Dr. Philip Zimbardo Revisits the Stanford Prison Experiment.”  Pacific Standard , 20 Jul. 2015, psmag.com/social-justice/philip-zimbardo-revisits-the-stanford-prison-experiment .
• Konnikova, Maria. “The Real Lesson of the Stanford Prison Experiment.”  The New Yorker , 12 June 2015, www.newyorker.com/science/maria-konnikova/the-real-lesson-of-the-stanford-prison-experiment .
• “Philip G. Zimbardo: Stanford Prison Experiment.”  Stanford Libraries, exhibits.stanford.edu/spe/about/philip-g-zimbardo .
• Ratnesar, Romesh. “The Menace Within.”  Stanford Alumni , July/Aug. 2011, alumni.stanford.edu/get/page/magazine/article/?article_id=40741 .
• Slavich, George M. “On 50 Years of Giving Psychology Away: An Interview with Philip Zimbardo.”  Teaching of Psychology , vol. 36, no. 4, 2009, pp. 278-284, DOI: 10.1080/00986280903175772, www.georgeslavich.com/pubs/Slavich_ToP_2009.pdf .
• Toppo, Greg. “Time to Dismiss the Stanford Prison Experiment?” Inside Higher Ed,  2018, June 20,  https://www.insidehighered.com/news/2018/06/20/new-stanford-prison-experiment-revelations-question-findings .
• Zimbardo, Philip G. “Philip G. Zimbardo.”  Social Psychology Network , 8 Sep. 2016, zimbardo.socialpsychology.org/ .
• Zimbardo, Philip G. “ The Psychology of Evil. ”  TED , Feb. 2008.
• Zimbardo, Philip G. “ The Psychology of Time. ”  TED , Feb. 2009.
• Zimbardo, Philip G. “What Makes a Hero?”  Greater Good Science Center , 18 Jan. 2011, greatergood.berkeley.edu/article/item/what_makes_a_hero .
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The Stanford Prison Experiment was massively influential. We just learned it was a fraud.

The most famous psychological studies are often wrong, fraudulent, or outdated. Textbooks need to catch up. 

by Brian Resnick

The Stanford Prison Experiment, one of the most famous and compelling psychological studies of all time, told us a tantalizingly simple story about human nature.

The study took paid participants and assigned them to be “inmates” or “guards” in a mock prison at Stanford University. Soon after the experiment began, the “guards” began mistreating the “prisoners,” implying evil is brought out by circumstance. The authors, in their conclusions, suggested innocent people, thrown into a situation where they have power over others, will begin to abuse that power. And people who are put into a situation where they are powerless will be driven to submission, even madness.

The Stanford Prison Experiment has been included in many, many introductory psychology textbooks and is often cited uncritically . It’s the subject of movies, documentaries, books, television shows, and congressional testimony .

But its findings were wrong. Very wrong. And not just due to its questionable ethics or lack of concrete data — but because of deceit.

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

A new exposé published by Medium based on previously unpublished recordings of Philip Zimbardo, the Stanford psychologist who ran the study, and interviews with his participants, offers convincing evidence that the guards in the experiment were coached to be cruel. It also shows that the experiment’s most memorable moment — of a prisoner descending into a screaming fit, proclaiming, “I’m burning up inside!” — was the result of the prisoner acting. “I took it as a kind of an improv exercise,” one of the guards told reporter Ben Blum . “I believed that I was doing what the researchers wanted me to do.”

The findings have long been subject to scrutiny — many think of them as more of a dramatic demonstration , a sort-of academic reality show, than a serious bit of science. But these new revelations incited an immediate response. “We must stop celebrating this work,” personality psychologist Simine Vazire tweeted , in response to the article . “It’s anti-scientific. Get it out of textbooks.” Many other psychologists have expressed similar sentiments.

( Update : Since this article published, the journal American Psychologist has published a thorough debunking of the Stanford Prison Experiment that goes beyond what Blum found in his piece. There’s even more evidence that the “guards” knew the results that Zimbardo wanted to produce, and were trained to meet his goals. It also provides evidence that the conclusions of the experiment were predetermined.)

Many of the classic show-stopping experiments in psychology have lately turned out to be wrong, fraudulent, or outdated. And in recent years, social scientists have begun to reckon with the truth that their old work needs a redo, the “ replication crisis .” But there’s been a lag — in the popular consciousness and in how psychology is taught by teachers and textbooks. It’s time to catch up.

Many classic findings in psychology have been reevaluated recently

The Zimbardo prison experiment is not the only classic study that has been recently scrutinized, reevaluated, or outright exposed as a fraud. Recently, science journalist Gina Perry found that the infamous “Robbers Cave“ experiment in the 1950s — in which young boys at summer camp were essentially manipulated into joining warring factions — was a do-over from a failed previous version of an experiment, which the scientists never mentioned in an academic paper. That’s a glaring omission. It’s wrong to throw out data that refutes your hypothesis and only publicize data that supports it.

Perry has also revealed inconsistencies in another major early work in psychology: the Milgram electroshock test, in which participants were told by an authority figure to deliver seemingly lethal doses of electricity to an unseen hapless soul. Her investigations show some evidence of researchers going off the study script and possibly coercing participants to deliver the desired results. (Somewhat ironically, the new revelations about the prison experiment also show the power an authority figure — in this case Zimbardo himself and his “warden” — has in manipulating others to be cruel.)

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

Other studies have been reevaluated for more honest, methodological snafus. Recently, I wrote about the “marshmallow test,” a series of studies from the early ’90s that suggested the ability to delay gratification at a young age is correlated with success later in life . New research finds that if the original marshmallow test authors had a larger sample size, and greater research controls, their results would not have been the showstoppers they were in the ’90s. I can list so many more textbook psychology findings that have either not replicated, or are currently in the midst of a serious reevaluation.

• Social priming: People who read “old”-sounding words (like “nursing home”) were more likely to walk slowly — showing how our brains can be subtly “primed” with thoughts and actions.
• The facial feedback hypothesis: Merely activating muscles around the mouth caused people to become happier — demonstrating how our bodies tell our brains what emotions to feel.
• Stereotype threat: Minorities and maligned social groups don’t perform as well on tests due to anxieties about becoming a stereotype themselves.
• Ego depletion: The idea that willpower is a finite mental resource.

Alas, the past few years have brought about a reckoning for these ideas and social psychology as a whole.

Many psychological theories have been debunked or diminished in rigorous replication attempts. Psychologists are now realizing it's  more likely  that false positives will make it through to publication than inconclusive results. And they’ve realized that experimental methods commonly used just a few years ago aren’t rigorous enough. For instance, it used to be commonplace for scientists to publish experiments that sampled about 50 undergraduate students. Today, scientists realize this is a recipe for false positives , and strive for sample sizes in the hundreds and ideally from a more representative subject pool.

Nevertheless, in so many of these cases, scientists have moved on and corrected errors, and are still doing well-intentioned work to understand the heart of humanity. For instance, work on one of psychology’s oldest fixations — dehumanization, the ability to see another as less than human — continues with methodological rigor, helping us understand the modern-day maltreatment of Muslims and immigrants in America.

In some cases, time has shown that flawed original experiments offer worthwhile reexamination. The original Milgram experiment was flawed. But at least its study design — which brings in participants to administer shocks (not actually carried out) to punish others for failing at a memory test — is basically repeatable today with some ethical tweaks.

And it seems like Milgram’s conclusions may hold up: In a recent study, many people found demands from an authority figure to be a compelling reason to shock another. However, it’s possible, due to something known as the file-drawer effect, that failed replications of the Milgram experiment have not been published. Replication attempts at the Stanford prison study, on the other hand, have been a mess .

In science, too often, the first demonstration of an idea becomes the lasting one — in both pop culture and academia. But this isn’t how science is supposed to work at all! 

Science is a frustrating, iterative process. When we communicate it, we need to get beyond the idea that a single, stunning study ought to last the test of time. Scientists know this as well, but their institutions have often discouraged them from replicating old work, instead of the pursuit of new and exciting, attention-grabbing studies. (Journalists are part of the problem too , imbuing small, insignificant studies with more importance and meaning than they’re due.)

Thankfully, there are researchers thinking very hard, and very earnestly, on trying to make psychology a more replicable, robust science. There’s even a whole Society for the Improvement of Psychological Science devoted to these issues.

Follow-up results tend to be less dramatic than original findings , but they are more useful in helping discover the truth. And it’s not that the Stanford Prison Experiment has no place in a classroom. It’s interesting as history. Psychologists like Zimbardo and Milgram were highly influenced by World War II. Their experiments were, in part, an attempt to figure out why ordinary people would fall for Nazism. That’s an important question, one that set the agenda for a huge amount of research in psychological science, and is still echoed in papers today.

Textbooks need to catch up

Psychology has changed tremendously over the past few years. Many studies used to teach the next generation of psychologists have been intensely scrutinized, and found to be in error. But troublingly, the textbooks have not been updated accordingly .

That’s the conclusion of a 2016 study in Current Psychology. “ By and large,” the study explains (emphasis mine):

introductory textbooks have difficulty accurately portraying controversial topics with care or, in some cases, simply avoid covering them at all. ... readers of introductory textbooks may be unintentionally misinformed on these topics.

The study authors — from Texas A&M and Stetson universities — gathered a stack of 24 popular introductory psych textbooks and began looking for coverage of 12 contested ideas or myths in psychology.

The ideas — like stereotype threat, the Mozart effect , and whether there’s a “narcissism epidemic” among millennials — have not necessarily been disproven. Nevertheless, there are credible and noteworthy studies that cast doubt on them. The list of ideas also included some urban legends — like the one about the brain only using 10 percent of its potential at any given time, and a debunked story about how bystanders refused to help a woman named Kitty Genovese while she was being murdered.

The researchers then rated the texts on how they handled these contested ideas. The results found a troubling amount of “biased” coverage on many of the topic areas.

But why wouldn’t these textbooks include more doubt? Replication, after all, is a cornerstone of any science.

One idea is that textbooks, in the pursuit of covering a wide range of topics, aren’t meant to be authoritative on these individual controversies. But something else might be going on. The study authors suggest these textbook authors are trying to “oversell” psychology as a discipline, to get more undergraduates to study it full time. (I have to admit that it might have worked on me back when I was an undeclared undergraduate.)

There are some caveats to mention with the study: One is that the 12 topics the authors chose to scrutinize are completely arbitrary. “And many other potential issues were left out of our analysis,” they note. Also, the textbooks included were printed in the spring of 2012; it’s possible they have been updated since then.

Recently, I asked on Twitter how intro psychology professors deal with inconsistencies in their textbooks. Their answers were simple. Some say they decided to get rid of textbooks (which save students money) and focus on teaching individual articles. Others have another solution that’s just as simple: “You point out the wrong, outdated, and less-than-replicable sections,” Daniël Lakens , a professor at Eindhoven University of Technology in the Netherlands, said. He offered a useful example of one of the slides he uses in class.

Anecdotally, Illinois State University professor Joe Hilgard said he thinks his students appreciate “the ‘cutting-edge’ feeling from knowing something that the textbook didn’t.” (Also, who really, earnestly reads the textbook in an introductory college course?)

And it seems this type of teaching is catching on. A (not perfectly representative) recent survey of 262 psychology professors found more than half said replication issues impacted their teaching . On the other hand, 40 percent said they hadn’t. So whether students are exposed to the recent reckoning is all up to the teachers they have.

If it’s true that textbooks and teachers are still neglecting to cover replication issues, then I’d argue they are actually underselling the science. To teach the “replication crisis” is to teach students that science strives to be self-correcting. It would instill in them the value that science ought to be reproducible.

Understanding human behavior is a hard problem. Finding out the answers shouldn’t be easy. If anything, that should give students more motivation to become the generation of scientists who get it right.

“Textbooks may be missing an opportunity for myth busting,” the Current Psychology study’s authors write. That’s, ideally, what young scientist ought to learn: how to bust myths and find the truth.

Further reading: Psychology’s “replication crisis”

• The replication crisis, explained. Psychology is currently undergoing a painful period of introspection. It will emerge stronger than before.
• The “marshmallow test” said patience was a key to success. A new replication tells us s’more.
• The 7 biggest problems facing science, according to 270 scientists
• What a nerdy debate about p-values shows about science — and how to fix it
• Science is often flawed. It’s time we embraced that.

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