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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.

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Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

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

On This Page:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Asserting Authority

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

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

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

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

Physical Punishment

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

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

Asserting Independence

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

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

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

Putting Down the Rebellion

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

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

Special Privileges

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

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

Consequences of the Rebellion

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

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

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

Prisoner #8612

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

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

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

A Visit from Parents

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

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

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

Catholic Priest

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

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

Prisoner #819

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

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

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

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

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

Back to Reality

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

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

An End to the Experiment

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Critical Evaluation

Ecological validity.

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

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

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

Demand characteristics

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

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

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

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

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

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

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

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

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

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

Sample bias

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

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

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

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

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

Zimbardo’s conclusion may be wrong

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

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

Contributions to psychology

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

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

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

Contribution to prison policy

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

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

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

The authors argue psychologists should reengage to:

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

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

Evidence for situational factors

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

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

Evidence for an interactionist approach

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

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

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

Ethical Issues

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

Protection of Participants

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

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

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

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

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

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

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

Withdrawal 

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

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

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

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

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

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

Discussion Questions

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

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

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

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

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

Frequently Asked Questions

What happened to prisoner 8612 after the experiment.

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

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

Why did Zimbardo not stop the experiment?

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

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

What happened to the guards in the Stanford Prison Experiment?

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

What did Zimbardo want to find out?

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

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

What were the results of the Stanford Prison Experiment?

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

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

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

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

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

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

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

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

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

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

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

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

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

Further Information

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

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The Stanford Prison Experiment

• Participants
• Setting and Procedure

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

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

Purpose of the Stanford Prison Experiment

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

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

Participants in the Stanford Prison Experiment

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

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

Setting and Procedures

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

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

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

Results of the Stanford Prison Experiment

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

It was noted that:

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

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

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

Impact of the Zimbardo Prison Experiment

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

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

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

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

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

Criticisms of the Stanford Prison Experiment

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

Ethical Issues

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

Why was Zimbardo's experiment unethical?

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

Lack of Generalizability

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

Lack of Realism

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

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

Recent Criticisms

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

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

Among the issues described:

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

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

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

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

Stanford University. About the Stanford Prison Experiment .

Stanford Prison Experiment. 2. Setting up .

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

Ratnesar R. The menace within . Stanford Magazine.

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

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

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

American Psychological Association. Ecological validity .

Blum B. The lifespan of a lie . Medium .

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

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

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

Demonstrating the Power of Social Situations via a Simulated Prison Experiment

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

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

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

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

Significance

Practical application.

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

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

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

Cited Research

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

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

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

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

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

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

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

American Psychological Association, June 8, 2004

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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.

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In This Article Expand or collapse the "in this article" section Stanford Prison Experiment (SPE): Icon and Controversy

Introduction, archival sources.

• Primary Documentation of the SPE
• Biographical Background
• SPE and Related Experiments in Media
• SPE in Textbooks, Handbooks, and Histories of Psychology
• Replication of the SPE and Related Replications
• Psychological Prison and Punishment Literature Related to the SPE
• Methodological Criticisms
• Ethical Criticisms
• Thibault Le Texier

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Stanford Prison Experiment (SPE): Icon and Controversy by David C. Devonis LAST REVIEWED: 26 August 2020 LAST MODIFIED: 26 August 2020 DOI: 10.1093/obo/9780199828340-0269

The Stanford Prison Experiment (SPE) took place at a time when the sources of authoritarianism and evil were a focal concern in psychology. It emerged from a tradition of activist social psychological research beginning with Solomon Asch in the 1940s and extending through Stanley Milgram’s obedience experiments in the early 1960s. The SPE was a product of the research program of social psychologist Philip Zimbardo, a member of the Stanford psychology faculty since 1968. Discussions among Zimbardo’s students in spring 1971 led to a plan to simulate a prison environment. They converted portions of the basement of a University building into a combination booking room and jail. Zimbardo and a number of his graduate and undergraduate students took on supervisory roles. Before the Experiment began, paid participants recruited through newspaper advertisements were screened to eliminate obvious psychopathology, then randomly assigned to either the role of ‘guard’ or ‘prisoner.’ On the first experimental morning August 14, 1971, actual local police simulated an arrest of each of the prisoner participants. After they arrived, blindfolded, a simulated booking took place. Guards escorted them to the prison hallway where prisoners were required to strip and exchange their clothing for simple shifts and slippers. After a simulated spray delousing, they entered makeshift cells. After this, the Experiment evolved as an extended improvisation, by both the guards and prisoners, on prison-related themes. Episodes of deprivation, bullying, and humiliation emerged unplanned. Originally planned to run for two weeks, the Experiment lasted only six days, prematurely terminated when its supervising personnel judged that the simulation had gotten out of their control. The coincidence of its termination with the Attica prison uprising in New York led to its immediate dissemination in the news. Since then the SPE has become one of the most iconic psychological studies of psychology’s modern era. Although intended to expose and ameliorate bad prison conditions, its effectiveness in this regard diminished during a rapid shift in US prison policy, in the mid-1970’s, from reform to repression. Over succeeding decades, the Experiment continued to stimulate the popular imagination, leading to an extensive replication on British television and its portrayal in two feature films. Soon after its original publication, the SPE attracted criticisms of its methodology. After 2010, critical scrutiny of the SPE as well as similar iconic studies from the 1960s and 1970s increased, fueled by the growing ‘replication crisis’ in psychology. This most recent phase of criticism reflects not just a turn toward reflexive disciplinary self-criticism but also the increased availability of archival sources for examination. The SPE continues to excite both passionate support and equally passionate obloquy, much as have other comparable simulations of human social behavior.

Philip Zimbardo, the primary investigator of the SPE, has been unusually generous in making archival donations during his lifetime. Two of these are physical archives in two different locations: the Zimbardo (Philip G.) Papers at the Stanford University Archives and the Philip Zimbardo Papers at the Drs. Nicholas and Dorothy Cummings Center for the History of Psychology (CCHP) at the University of Akron. Alongside these is a virtual archive, the Stanford Prison Experiment website, maintained for over twenty years by Zimbardo and others. The Stanford Prison Experiment: 40 Years Later , a website constructed by the Stanford University archivist in connection with an exhibition at Stanford, contains links to much of the transcribed data collected by Zimbardo and his colleagues in 1971. Le Texier 2018 and Le Texier 2019 (cited under Thibault Le Texier ) represent the most complete use of the archives to date, and citations in these critiques of the SPE form a virtual finding aid for the many subdivisions of the available archival material.

Philip Zimbardo Papers. Drs. Nicholas and Dorothy Cummings Center for the History of Psychology (CCHP). Univ. of Akron, Akron, Ohio.

This collection, a subset (4.5 linear feet in 16 boxes) of the Stanford Zimbardo archive, is focused on the SPE. It contains SPE-specific materials, teaching materials, and materials relating to the development of Zimbardo 2008 (cited under Primary Documentation of the SPE ). The CCHP also holds several oversize folders of SPE materials and has some of the original props and costumes from the SPE. The finding aid also has a brief Zimbardo biography. The finding aid is available online .

The Stanford Prison Experiment .

Well-designed and informative website, maintained with National Science Foundation (NSF) funding under sponsorship of the Social Psychology Network, with links to much of the primary documentary and contextual material relating to the SPE as well as to major media presentations of the Experiment. Historically it evolved from the original slide show Zimbardo and White 1972 (cited under SPE and Related Experiments in Media ) circulated among social psychologists in the 1970s.

The Stanford Prison Experiment: 40 Years Later In Stanford Libraries: Special Collections and University Archives .

This site contains copies of material related to the SPE from the Stanford Archives, including accessible transcripts of several documents related to the SPE such as the original informed consent forms, audio clips, and photos, as well as links to the original eighty-slide slideshow from the 1970s.

Zimbardo (Philip G.) Papers. Stanford University Archives, Collection SC0750.

This collection runs 256 linear feet in 182 boxes, and contains material directly and peripherally related to the SPE, including a substantial amount of audiovisual and film material and materials used in Zimbardo’s classes at Stanford. The finding aid, available online , has a brief Zimbardo biography attached.

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Frequently asked questions.

This page offers brief answers to some of the most frequently asked questions about the Stanford Prison Experiment:

About the Study

About the Prisoners

About the Guards

Research Ethics

Aftermath of the Study

About the Website

ABOUT THE STUDY

Q:  What was the purpose of the Stanford Prison Experiment?

A:   The purpose was to understand the development of norms and the effects of roles, labels, and social expectations in a simulated  prison environment.

Q:  Who funded the experiment?

A:   The study was funded by a government grant from the U.S. Office of Naval Research to study antisocial behavior.

Q:  How were participants recruited?

A:   The research team placed newspaper advertisements in the Palo Alto Times and The Stanford Daily offering $15/day to male college students for a study on the psychology of imprisonment.

Q:  What were students told before the study began?

A:   Students were told that they would be assigned to play the role of prisoner or guard in a study of prison life, that they would observed and filmed, and that they would be expected to participate for the full duration of the study (see  Description of Study Given to Applicants ).

Q:  Who participated in the experiment?

A:    From more than 75 people who responded to the ad, 24 students were chosen: 12 to role play prisoners (9 plus 3 alternates) and 12 to role play guards (also 9 plus 3 alternates). These students had no prior record of criminal arrests, medical conditions, or psychological disorders.

Q:  How were students assigned to the role of prisoner or guard?

A:   The assignment was done randomly, as with the toss of a coin, to make sure that the prisoners and guards were comparable to each other at the beginning of the experiment.

Q:  Did participants live in the prison 24 hours per day?

A:   Prisoners remained in the prison throughout the day and night, but guards generally rotated in three 8-hour shifts. Thus, there were typically three students guarding nine prisoners.

Q:  What were the main results?

A:   There were many results, but perhaps the most important was simply this: The simulation became so real, and the guards became so abusive, that the experiment had to be shut down after only 6 days rather than the two weeks planned.

Q:  How does the movie differ from the actual Stanford Prison Experiment?

A:  Although the Stanford Prison Experiment movie was inspired by the classic 1971 experiment, there are key differences between the two. In the actual experiment, guards and prisoners were prevented from carrying out acts of physical violence such as those shown in the movie. In addition, the study ended differently than the movie. In the actual study, Professor Zimbardo's former graduate student (and future wife) Christina Maslash confronted him and said that by taking on the role of prison superintendent, he had become indifferent to the suffering of his participants. He then realized that she was right and announced that he would end the experiment the next day. The movie depicts this confrontation, but to heighten the drama, Professor Zimbardo is shown returning to the experiment and observing guards sexually humiliate the prisoners, after which he immediately ends the study.

ABOUT THE PRISONERS

Q:  How did the prisoner arrests take place?

A:   The Palo Alto police conducted surprise arrests at the home of prisoners. Students were handcuffed, searched, read their rights, and driven in a squad car to the police station for booking and fingerprinting. The first five prisoners were charged with burglary, and the last four were charged with armed robbery.

Q:  What rules were the prisoners required to follow?

A:   The prison warden and guards drew up a list of rules that prisoners were required to follow, such as remaining silent during rest periods, eating at meal times, and keeping the prison cells clean (see  Prisoner Rules ).

Q:  Were prisoners allowed to quit the experiment?

A:   Yes, and some prisoners did discontinue their participation. For the most part, however, prisoners seemed to forget or misunderstand that they could leave "through established procedures," and they reinforced a sense of imprisonment by telling each other that there was no way out.

Q:  How many prisoners left the experiment early?

A:    Half the prisoners were released early due to severe emotional or cognitive reactions.

ABOUT THE GUARDS

Q:  Were the guards given any special training?

A:    No. The guards were given only a brief orientation telling them to maintain law and order, avoid physical violence, and prevent prisoner escapes.

Q:  Did personality scores predict which guards were most abusive?

A:   No. The most and least abusive guards did not differ significantly in authoritarianism, Machiavellianism, or other personality measures. Abusive guard behavior appears to have been triggered by features of the situation rather than by the personality of guards.

Q:  How many guards left the experiment early?

A:    None, although one guard later said that he had considered it.

RESEARCH ETHICS

Q:  Did students give informed consent before participating?

A:   Yes, all students signed a  Consent Form  before participating in the study.

Q:  Was the Stanford Prison Experiment approved by an Institutional Review Board?

A:   Yes, the study was approved by the Stanford  Human Subjects Review Committee , the Stanford Psychology Department, and the Group Effectiveness Branch of the Office of Naval Research. In addition, the Student Health Department was alerted to the study and prior arrangements were made for any medical care the participants might need.

Q:  Did the APA ever review the experiment's ethics?

A:   Yes. In 1973 Professor Zimbardo asked the American Psychological Association to conduct an ethics evaluation, and the APA concluded that all existing ethical guidelines had been followed.

Q:  Has Professor Zimbardo ever apologized for the suffering that occurred?

A:   Yes. In his book  The Lucifer Effect , Professor Zimbardo wrote: "I was guilty of the sin of omission -- the evil of inaction -- of not providing adequate oversight and surveillance when it was required... the findings came at the expense of human suffering. I am sorry for that and to this day apologize for contributing to this inhumanity." (pp. 181, 235)

AFTERMATH OF THE STUDY

Q:  Did any of the participants suffer lasting trauma?

A:   Despite suffering extreme emotional stress during the experiment, all participants appear to have regained their baseline emotional states after the study. Extensive follow-up testing revealed no lasting trauma to participants.

Q:  After the study ended, what became of the experimenters?

A:   All went on to distinguished careers in psychology or medicine:

David Jaffe, an undergraduate research associate who played the role of prison warden, is now a professor of pediatrics at Washington University.

Curtis Banks, a graduate student researcher, became the first African American psychology professor to receive tenure at Princeton University.

Craig Haney , a graduate student researcher, became a psychology professor at UC--Santa Cruz and is a leading expert on prison conditions.

Christina Maslach , a former graduate student who helped end the study early, became a psychology professor and vice provost at UC--Berkeley.

Philip Zimbardo , who served as principle investigator and prison superintendent, became APA President in 2001 and is now a professor emeritus at Stanford University.

Q:  Are materials from the experiment archived anywhere?

A:   Yes, materials from the experiment have been preserved by the Center for the History of Psychology and the Stanford University Archives .

ABOUT THE WEBSITE

Q:  Who designed this website?

A:   The website was originally designed by Scott Plous and Mike Lestik in 1999. The site was redesigned in 2015 by Jeff Breil, Scott Plous, and David Jensenius.

Q:   Who manages the website?

A:   The site is managed by Social Psychology Network (SPN), a nonprofit educational organization headquartered at Wesleyan University in Middletown, Connecticut.

Q:   Who funds the website?

A:   The site is funded with generous support from the National Science Foundation (grants #9950517, #0339002, #0843855, and #1456048), SPN members, and other sources. As an Amazon Associate, this site also receives revenue from qualified purchases. To support this website or join Social Psychology Network, please visit the SPN Membership page.

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

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

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

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

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

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The Real Lesson of the Stanford Prison Experiment

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The experiment generated important research into unexplored territories..

Posted August 16, 2021 | Reviewed by Tyler Woods

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

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

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

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

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

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

The Experiment in a Nutshell

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

Challenging the Truth

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

Denial and Finger Pointing

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

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

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

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

“The Stanford Prison Experiment” Film

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

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

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

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

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

Heroic Imagination

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

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

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The Stanford Prison Experiment: The Power of the Situation

• First Online: 20 January 2024

Cite this chapter

• 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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Alexander, M. (2001, August 22). Thirty years later, Stanford Prison Experiment lives on. Stanford Report . Accessed April 22, 2022, from https://news.stanford.edu/news/2001/august22/prison2-822.html?msclkid=7d17df2ec26f11ec8086da6bf715d359

Amdur, R. J. (2006). Provisions for data monitoring. In E. A. Bankert, & J. R. Amdur (Eds.), Institutional review board: Management and function , 2nd edition (pp. 160–165). Jones & Bartlet

Google Scholar  

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

Article   Google Scholar  

Blau, P. M. (1964). Exchange and power in social life . Wiley.

Farkas, M. A. (2000). A typology of correctional officers. International Journal of Offender Therapy and Comparative Criminology, 44 (4), 431–449. https://doi.org/10.1177/0306624X00444003

Festinger, L., Pepitone, A., & Newcombe, T. (1952). Some consequences of deindividuation in a group. Journal of Abnormal and Social Psychology, 47 , 382–389.

French, J. R. P., & Raven, B. (1959). The bases of social power. In D. Cartwright (Ed.), Studies in social power (pp. 150–167). Institute for Social Research.

Frohnmayer, D. (2004, November 30). “Situational ethics, social deception, and lessons of machiavelli” Judge learned hand award Luncheon Oregon chapter of the American Jewish Committee Tuesday . http://president.uoregon.edu/speeches/situationalethics.shtml

Goffman, E. (1961). Asylums. Essays on the social situation of mental patients and other inmates . Doubleday Anchor. http://www.diligio.com/goffman.htm

Gross, B. (2008, Winter/December). Prison violence: Does brutality come with the badge? The Forensic Examiner . http://www.theforensicexaminer.com/archive/winter08/6/

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

Lovibond, S. H., Mithiran, & Adams, W. G. (1979). Effects of three experimental prison environments on the behaviour of non-convict volunteer subjects. Australian Psychologist, 14 (3), 273–285.

Maslach, C. (1971). The “truth” about false confessions. The Journal of Personality and Social Psychology, 20 (2), 141–146. https://doi.org/10.1037/h0031675

Maslach, C. (1974). Social and personal bases of individuation. Journal of Personality and Social Psychology, 29 (3), 411–425. https://doi.org/10.1037/h0036031

Maslach, C., Marshall, G., & Zimbardo, P. G. (1972). Hypnotic control of peripheral skin temperature: A case report. Psychophysiology, 9 (6), 600–605. https://doi.org/10.1111/j.1469-8986.1972.tb00769.x

Morgan, A. H., Lovibond, S. H., & Adams, W. G. (1979). Comments on S. H. Lovibond, Mithiran, & W. G. Adams: “The effects of three experimental prison environments on the behaviour of non-convict volunteer subjects”. Australian Psychologist, 14 (3), 273–287.

NHLBI. (2008). National Heart Lung and Blood Institute. Data and safety monitoring policy . http://www.nhlbi.nih.gov/funding/policies/dsmpolicy.htm

O’Toole, K. (1997, January 8). The Stanford prison experiment: Still powerful after all these years. Stanford report . Stanford University News Service. http://www.stanford.edu/news/gif/snewshd.gif

Prescott, C. (2005, April 28). The lie of the Stanford prison experiment. The Stanford Daily .

Sawyer, K. D. (2021). George Jackson, 50 years later . Accessed January 18, 2022, from https://sfbayview.com/2021/08/george-jackson-50-years-later/?msclkid=4afbd2c7c26b11eca875b013aedf20b3

Schaufeli, W. B., & Peeters, M. C. W. (2000). Job stress and burnout among correctional officers: A literature review. International Journal of Stress Management, 7 (1), 19–48. https://doi.org/10.1023/A:1009514731657

Schlesinger Report. (2004). Final report of the independent panel to review Department of Defense Detention Operations . http://news.bbc.co.uk/nol/shared/bsp/hi/pdfs/24_08_04_abughraibreport.pdf

SPE Website. (n.d.). Stanford Prison Experiment Website. The story: An overview of the experiment . Accessed February 28, 2022, from https:// www.prisonexp.org/the-story

Weber, M. (1947). The theory of social and economic organization . Oxford University Press.

Zimbardo, P. (1969). The human choice: Individuation, reason and order versus deindividuation, impulse, and chaos. In W. J. Arnold & D. Levine (Eds.), Nebraska Symposium on Motivation (Vol. 17, pp. 237–307). University of Nebraska Press.

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

Zimbardo, P. G., Marshall, C., White, G., & Maslach, C. (1973). Objective assessment of hypnotically induced time distortion. Science, 181 (4096), 282–284.

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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Acknowledgments

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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Table of Contents

Background and Objectives

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

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

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

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

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

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

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

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

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

Methodology

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

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

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

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

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

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

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

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

The study was scheduled to run for 14 days.

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

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

Findings and Analysis

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

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

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

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

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

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

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

Some prisoners began showing signs of depression and acute anxiety .

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

Prisoner #819 was then subjected to further abuse.

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

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

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

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

Criticisms and Ethical Concerns

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

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

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

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

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

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

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

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

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

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

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

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

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

Legacy and Relevance Today

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

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

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

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

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

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

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

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

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

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

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

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

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The Menace Within

What happened in the basement of the psych building 40 years ago shocked the world. how do the guards, prisoners and researchers in the stanford prison experiment feel about it now.

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Photo: Stanford Prison Experiment

By Romesh Ratnesar

IT BEGAN WITH AN AD in the classifieds.

Male college students needed for psychological study of prison life. $15 per day for 1-2 weeks. More than 70 people volunteered to take part in the study, to be conducted in a fake prison housed inside Jordan Hall, on Stanford's Main Quad. The leader of the study was 38-year-old psychology professor Philip Zimbardo . He and his fellow researchers selected 24 applicants and randomly assigned each to be a prisoner or a guard.

Zimbardo encouraged the guards to think of themselves as actual guards in a real prison. He made clear that prisoners could not be physically harmed, but said the guards should try to create an atmosphere in which the prisoners felt "powerless."

The study began on Sunday, August 17, 1971. But no one knew what, exactly, they were getting into.

Forty years later, the Stanford Prison Experiment remains among the most notable—and notorious—research projects ever carried out at the University. For six days, half the study's participants endured cruel and dehumanizing abuse at the hands of their peers. At various times, they were taunted, stripped naked, deprived of sleep and forced to use plastic buckets as toilets. Some of them rebelled violently; others became hysterical or withdrew into despair. As the situation descended into chaos, the researchers stood by and watched—until one of their colleagues finally spoke out.

The public's fascination with the SPE and its implications—the notion, as Zimbardo says, "that these ordinary college students could do such terrible things when caught in that situation"—brought Zimbardo international renown. It also provoked criticism from other researchers, who questioned the ethics of subjecting student volunteers to such extreme emotional trauma. The study had been approved by Stanford's Human Subjects Research Committee, and Zimbardo says that "neither they nor we could have imagined" that the guards would treat the prisoners so inhumanely.

In 1973, an investigation by the American Psychological Association concluded that the prison study had satisfied the profession's existing ethical standards. But in subsequent years, those guidelines were revised to prohibit human-subject simulations modeled on the SPE. "No behavioral research that puts people in that kind of setting can ever be done again in America," Zimbardo says.

The Stanford Prison Experiment became the subject of numerous books and documentaries, a feature film and the name of at least one punk band. In the last decade, after the revelations of abuses committed by U.S. military and intelligence personnel at prisons in Iraq and Afghanistan, the SPE provided lessons in how good people placed in adverse conditions can act barbarically.

The experiment is still a source of controversy and contention—even among those who took part in it. Here, in their own words, some of the key players in the drama reflect on their roles and how those six days in August changed their lives.

The Superintendent

Phil Zimbardo Zimbardo joined Stanford's psychology department in 1968 and taught there until his retirement in 2007.

The study was focused originally on how individuals adapt to being in a relatively powerless situation. I was interested in prisoners and was not really interested in the guards. It was really meant to be a single, dramatic demonstration of the power of the situation on human behavior. We expected that we would write some articles about it and move on.

After the end of the first day, I said, "There's nothing here. Nothing's happening." The guards had this antiauthority mentality. They felt awkward in their uniforms. They didn't get into the guard mentality until the prisoners started to revolt. Throughout the experiment, there was this conspiracy of denial—everyone involved was in effect denying that this was an experiment and agreeing that this is a prison run by psychologists.

There was zero time for reflection. We had to feed the prisoners three meals a day, deal with the prisoner breakdowns, deal with their parents, run a parole board. By the third day I was sleeping in my office. I had become the superintendent of the Stanford county jail. That was who I was: I'm not the researcher at all. Even my posture changes—when I walk through the prison yard, I'm walking with my hands behind my back, which I never in my life do, the way generals walk when they're inspecting troops.

We had arranged for everyone involved—the prisoners, guards and staff—to be interviewed on Friday by other faculty members and graduate students who had not been involved in the study. Christina Maslach, who had just finished her PhD, came down the night before. She's standing outside the guard quarters and watches the guards line up the prisoners for the 10 o'clock toilet run. The prisoners come out, and the guards put bags over their heads, chain their feet together and make them put their hands on each other's shoulders, like a chain gang. They're yelling and cursing at them. Christina starts tearing up. She said, "I can't look at this."

I ran after her and we had this argument outside Jordan Hall. She said, "It's terrible what you're doing to these boys. How can you see what I saw and not care about the suffering?" But I didn't see what she saw. And I suddenly began to feel ashamed. This is when I realized I had been transformed by the prison study to become the prison administrator. At that point I said, "You're right. We've got to end the study."

[As the study was underway], there was an escape attempt at San Quentin prison and [former Black Panther] George Jackson was shot and killed. Three weeks after that, there's the Attica prison riot [in New York]. Suddenly, prisons are hot. Two government investigative committees start hearings and I'm flown out to Washington to present to a congressional subcommittee on the nature of prisons. I went from knowing nothing firsthand about prisons to being an expert. But I worked hard to learn more. I visited a number of correctional facilities all over the country. I organized a program for Stanford students to teach a course at a prison. For years I had an active correspondence with at least 20 different prisoners.

It wasn't a formal experiment. My colleagues probably never thought much of it. But as a result of the prison study, I really became more aware of the central role of power in our lives. I became more aware of the power I have as a teacher. I started consciously doing things to minimize the negative use of power in the classroom. I encouraged students to challenge me.

I think I became more self-reflective. I'm more generous and more open because of that experience. I think it made me a better person.

The Whistleblower .

Christina Maslach Maslach, PhD '71, became a professor at UC-Berkeley. She and Zimbardo married in 1972. They live in San Francisco.

I had just finished my doctorate and was about to leave Stanford to start my new job. Phil and I had started dating. The prison study was never anything I was considering playing a part in. During the first few days of the experiment, I did hear from Phil, but not in great detail. What I was getting, though, was a sense that it was becoming a real prison—people were not just fooling around but actually getting caught up in the situation. But it still wasn't evident to me what that might mean.

At first Phil didn't seem different. I didn't see any change in him until I actually went down to the basement and saw the prison. I met one guard who seemed nice and sweet and charming, and then I saw him in the yard later and I thought, "Oh my God, what happened here?" I saw the prisoners being marched to go down to the men's room. I was getting sick to my stomach, physically ill. I said, "I can't watch this." But no one else was having the same problem.

Phil came after me and said, "What's the matter with you?" That's when I had this feeling like, "I don't know you. How can you not see this?" It felt like we were standing on two different cliffs across a chasm. If we had not been dating before then, if he were just another faculty member and this happened, I might have said, "I'm sorry, I'm out of here" and just left. But because this was someone I was growing to like a lot, I thought that I had to figure this out. So I kept at it. I fought back, and ended up having a huge argument with him. I don't think we've ever had an argument quite like that since then.

I feared that if the study went on, he would become someone I no longer cared for, no longer loved, no longer respected. It's an interesting question: Suppose he kept going, what would I have done? I honestly don't know.

The clearest influence the study had on me was that it raised some really serious questions about how people cope with extremely emotional, difficult situations, especially when it's part of their job—when they have to manage people or take care of them or rehabilitate them. So I started interviewing people. I started with some prison guards in a real prison, and talked to them about their jobs and how they understood what they were doing. At first I wasn't sure what I was looking for. I was just trying to listen.

I interviewed people who worked in hospitals, in the ER. After a while I realized there was a rhythm and pattern emerging, and when I described it to someone they said, "I don't know what it's called in other professions, but in our occupation we call it 'burnout.'" And so I spent a good chunk of my professional life developing and defining what burnout is—what are the things that cause it and how can we intervene and help people cope with it more effectively. All of that work on burnout had some origins in the experience I had in the prison experiment.

People will sometimes come up to me—at conferences, or maybe they're students who have taken psychology classes—and they'll say, "Oh my God, you're such a hero! What is it like to be a hero?" And it's always a little surprising to me because it sure didn't feel heroic at the time. The prison study has given me a new understanding of what "heroism" means. It's not some egocentric, I'm-going-to-rush-into-that-burning-building thing—it's about seeing something that needs to be addressed and saying, I need to help and do something to make it better.

Dave Eshelman The son of a Stanford engineering professor, Eshelman was a student at Chapman University at the time of the experiment. He was the prison's most abusive guard, patterning himself after the sadistic prison warden (portrayed by Strother Martin) in the movie Cool Hand Luke. Today he owns a mortgage business in Saratoga.

I was just looking for some summer work. I had a choice of doing this or working at a pizza parlor. I thought this would be an interesting and different way of finding summer employment.

The only person I knew going in was John Mark. He was another guard and wasn't even on my shift. That was critical. If there were prisoners in there who knew me before they encountered me, then I never would have been able to pull off anything I did. The act that I put on—they would have seen through it immediately.

What came over me was not an accident. It was planned. I set out with a definite plan in mind, to try to force the action, force something to happen, so that the researchers would have something to work with. After all, what could they possibly learn from guys sitting around like it was a country club? So I consciously created this 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. 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?'" But the other guards didn't stop me. They seemed to join in. They were taking my lead. Not a single guard said, "I don't think we should do this."

The fact that I ramped up the intimidation and the mental abuse without any real sense as to whether I was hurting anybody? I definitely regret that. But in the long run, no one suffered any lasting damage. When the Abu Ghraib scandal broke, my first reaction was, this is so familiar to me. I knew exactly what was going on. I could picture myself in the middle of that and watching it spin out of control. When you have little or no supervision as to what you're doing, and no one steps in and says, "Hey, you can't do this"—things just keep escalating. You think, how can we top what we did yesterday? How do we do something even more outrageous? I felt a deep sense of familiarity with that whole situation.

Sometimes when people know about the experiment and then meet me, it's like, My God, this guy's a psycho! But everyone who knows me would just laugh at that.

John Mark Mark was about to begin his junior year at Stanford. He graduated in 1973 with a degree in anthropology. He lives in the Bay Area and has worked for the last 18 years as a medical coder for Kaiser Permanente.

I had spent my sophomore year at Stanford in France and returned to campus that spring. It was one of the most pivotal times in my life. Over Thanksgiving of the year before, I went with a friend to Amsterdam. You have to remember this is 1970, it was basically the '60s. We went to one of those clubs where you could buy drugs. We bought hash and actually brought some back with us, and I was caught at the French border. For a few hours I was told by French border guards that I was going to prison. In the end they let me go, but I definitely had been scared out of my wits.

When I saw this thing about a prison experiment, I thought I had some life experiences to bring to it. I felt this was going to be an important experiment. I told them all about what I'd been through and why it was important to me to be a prisoner. It was very disappointing to be assigned to be a guard, but I did the best I could.

During the day shift, when I worked, no one did anything that was beyond what you'd expect in a situation like that. But Zimbardo went out of his way to create tension. Things like forced sleep deprivation—he was really pushing the envelope. I just didn't like the whole idea of constantly disturbing people and asking them to recite their prisoner numbers in a count. I certainly didn't like when they put a guy in solitary confinement.

At that time of my life, I was getting high, all day every day. I got high before I went to the experiment; I got high on my breaks and lunch. I got high afterwards. I brought joints with me, and every day I wanted to give them to the prisoners. I looked at their faces and saw how they were getting dispirited and I felt sorry for them.

I didn't think it was ever meant to go the full two weeks. I think Zimbardo wanted to create a dramatic crescendo, and then end it as quickly as possible. I felt that throughout the experiment, he knew what he wanted and then tried to shape the experiment—by how it was constructed, and how it played out—to fit the conclusion that he had already worked out. He wanted to be able to say that college students, people from middle-class backgrounds—people 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. I don't think the actual events match up with the bold headline. I never did, and I haven't changed my opinion.

The Researchers

Craig Haney A graduate student of Zimbardo's, Haney, MA '71, PhD '78, JD '78, was responsible for overseeing the experiment and analyzing the data gathered from it. He went on to become a professor at UC-Santa Cruz, a leading authority on the psychological effects of incarceration and an advocate for prison reform.

What we thought we were going to find is that there would be subtle behavioral changes that would take place over time. There were moments, in the course of deciding about whether to do it, where we wavered. Not because we thought it would go too far or be too dramatic, but because we weren't sure anything was going to happen. I remember at one point asking, "What if they just sit around playing guitar for two weeks? What the hell are we going to do then?"

People have said to me, you must have known this was going to happen. We didn't—and we were not naive. We were very well read in the literature. We just did not anticipate these kinds of things happening. It really was a unique experience to watch human behavior transform in front of your eyes. And I can honestly say that I try never to forget it. I spend a lot of time with real prisoners and real guards, and having seen what I saw then, while a graduate student, gave me respect for the power of institutional environments to transform good people into something else.

I also realized how quickly we get used to things that are shocking one day and a week later become matter-of-fact. During the study, when we decided to move prisoners to different parts of the prison, we realized that they were going to see where they were and be reminded they're not in a prison—they're just in the psych building at Stanford. We didn't want that to happen.

So we put paper bags over their heads. The first time I saw that, it was shocking. By the next day we're putting bags on their heads and not thinking about it. That happens all the time in real correctional facilities. You get used to it. I do a lot of work in solitary-confinement units, on the psychological effects of supermax prisons. In places like that, when prisoners undergo the so-called therapy counseling, they are kept in actual cages. I constantly remind myself never to get used to seeing the cages.

The prisoners in this study were a downtrodden lot by the end of it. Even the guys who didn't break down were hurting. This was a really difficult experience. And for me that was a lesson, too. Real prisoners learn how to mask their pain and act like it doesn't matter. The prison study showed what it feels like for people who have not learned how to wear that implacable mask. I try to talk to prisoners about what their lives are really like, and I don't think I would have come to that kind of empathy had I not seen what I saw at Stanford. If someone had said that in six days you can take 10 healthy college kids, in good health and at the peak of resilience, and break them down by subjecting them to things that are commonplace and relatively mild by the standards of real prisons—I'm not sure I would have believed it, if I hadn't seen it happen.

The Prisoner

Richard Yacco A community college student at the time, Yacco helped instigate a revolt against conditions in Zimbardo's prison. He was released one day early from the study after exhibiting signs of depression. After working in radio and television production, he now teaches at a public high school in Oakland.

At the time I was debating: If I were drafted to fight in Vietnam, what would I do? Would I be willing to go to jail? Since that was one of the considerations, I thought, well, a prison experiment would give me some insight into what that would be like.

The first thing that really threw me off was the sleep deprivation. When they woke us up the first time, I had no idea it was after only four hours of sleep. It was only after they got us up and we did some exercises and then they let us go back to bed that I realized they were messing with our sleep cycles. That was kind of a surprise from the first night.

I don't recall exactly when the prisoners started rebelling. I do remember 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. It was that era. I had been willing to go on marches against the Vietnam war, I went on marches for civil rights, and was trying to figure out what I would do to resist even going into the service. So in a way I was testing some of my own ways of rebelling or standing up for what I thought was right.

My parents came on visitors' night. They were really concerned with the way I looked. I told them that they're breaking up our sleep, that we weren't having the chance to take showers. My appearance really concerned both of my parents, my mother especially.

When I asked [Zimbardo's team] what I could do if I wanted to quit, I was told, "You can't quit—you agreed to be here for the full experiment." That made me feel like a prisoner at that point. I realized I had made a commitment to something that I now could not change. I had made myself a prisoner.

I ended up being paroled by the "parole board." They released me Thursday night. That's when they told me they were going to end the experiment the next day. What I learned later is that the reason they chose me [to parole] is because they thought I'd be the next guy to break down. I was surprised, because I never thought I was going through any kind of depression or anything like that.

One thing that I thought was interesting about the experiment was whether, if you believe society has assigned you a role, do you then assume the characteristics of that role? I teach at an inner city high school in Oakland. These kids don't have to go through experiments to witness horrible things. But what frustrates my colleagues and me is that we are creating great opportunities for these kids, we offer great support for them, why are they not taking advantage of it? Why are they dropping out of school? Why are they coming to school unprepared? I think a big reason is what the prison study shows—they fall into the role their society has made for them.

Participating in the Stanford Prison Experiment is something I can use and share with students. This was one week of my life when I was a teenager and yet here it is, 40 years later, and it's still something that had enough of an impact on society that people are still interested in it. You never know what you're going to get involved in that will turn out to be a defining moment in your life.

Romesh Ratnesar , ’96, MA ’96,  is a former State Department official and a member of the editorial board of  Bloomberg View.  He lives in Washington, D.C.

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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.

Samples from the Collection

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What a widely attacked experiment got right on the harmful effects of prisons

Assistant Professor of Sociology, University of Toronto

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Ashley Rubin receives funding from the American Philosophical Society and the University of Toronto.

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The Stanford Prison Experiment is one of the few scientific studies to enter the public consciousness through mainstream news , documentaries , popular books , a TED talk and a major motion picture .

Recently, it has been making headlines in a very bad way.

In 1971, Stanford University psychology professor Philip Zimbardo sought to evaluate the prison’s impact on human behavior . He randomly assigned normal, healthy, emotionally stable male college students (without criminal records) to be “prisoners” or “guards” in a fake prison.

Within six days, Zimbardo ended the experiment. The “guards” were torturing the “prisoners,” and the “prisoners” were rebelling or experiencing psychological breakdown.

In news articles, the Stanford experiment has been “debunked” and “exposed as a fraud.” Its findings have been declared “very wrong” and “ fake .” It has been further criticized for experimenter interference, faked behaviour from participants and for research design problems, among other things.

These serious critiques have generated much discussion in academic circles and in news articles about what, if anything, we can learn from the experiment.

And yet, as someone who studies prisons, I’m struck by how much the Stanford Prison Experiment got right. A wealth of other research suggests prisons have serious detrimental effects on prisoners and prison workers alike.

What the research says

Living and working in prison is extremely stressful and demoralizing .

Some people are better at repelling these effects than others. Even so, prisoners and prison workers suffer from high rates of depression, anxiety, suicide, PTSD and other devastating conditions. For many prisoners, these conditions continue after prison and can be worsened by the transition into the free world .

We have long known that prisons are damaging places for both prisoners and prison workers. In his 1956 book, Society of Captives , Princeton sociology professor Gresham Sykes explained that incarceration deeply injured prisoners’ dignity and self-concept. He also described how prison officers became “corrupted” by the prison environment with its contradictory imperatives, impossible-to-enforce rules and necessary compromises.

In the 60 years since Sykes’ book, research in diverse prison settings has confirmed and expanded upon many of his findings.

The role of prison design

These insights extend beyond contemporary prisons in the United States. Prisons in Norway , Sweden and Denmark , known for their humaneness, also cause harm.

Indeed, smart designs can lessen , but not destroy, the prison’s negative impacts. But since the 1970s , in many Western countries, the main goal when designing prisons has been containment and security, not prisoners’ physical and mental health.

Popping up in the U.S. in the 1980s and 1990s, supermaximum security prisons (Supermaxes), which contain prisoners in solitary confinement in small concrete cells for 23 hours a day , are a particularly harmful design.

Read more: Broken system: Why is a quarter of Canada's prison population Indigenous?

Prisoners react differently to these Supermax prison regimes. Some are able to withstand the conditions, others break down within hours of their arrival. We do not yet fully understand why people react differently, but we do know that Supermax prisons have an array of negative impacts on prisoners’ mental health including hallucinations, self-harm and permanent psychological damage .

Not just prisoners

Prison staff are also affected. The history of American imprisonment is also filled with examples of people with good intentions becoming “corrupted” by the prison.

Pennsylvania’s Eastern State Penitentiary opened in 1829. Progressive Philadelphia penal reformers designed Eastern to be more humane than other prisons, with prisoners’ physical and mental health in mind. They implemented a routine — combining work, education, mentorship and outdoor exercise — to benefit both prisoners and society. Finally, they sought to protect prisoners’ identities so they could reenter society without stigma.

Within five years of the prison’s opening, however, the penal reformers, now prison administrators, had betrayed their humanitarian goals.

They bent the rules , out of necessity or convenience, so the prison functioned smoothly. In the process, they sacrificed the regime’s humanitarian and prisoner-focused elements.

Eastern’s administrators authorized torture , including what we now call waterboarding, held misbehaving prisoners after their sentences had expired until they apologized and justified these actions as beneficial to prisoners.

These gaps between theory and practice, including the use of torture punishments, were common at other American prisons in the 19th century and into the 20th. Other penal reformers–turned-administrators engaged in similar malfeasance despite their apparently genuine commitment to humanitarian values.

The situation was even more dire at prisons that were explicitly designed to be punitive and lacked Eastern’s humanitarian motivations .

Beyond the Stanford experiment

Even including these past failures, modern prisons rarely devolve as quickly and decidedly into a den of overt torture and serious mental breakdown as seen in the “Stanford Prison.”

It does happen — the Abu Ghraib torture scandal and the retaking of Attica Prison following the 1971 riot are graphic illustrations of how prison can unleash the worst of human nature with terrible consequences — but such extreme cases remain rare. Prisons’ negative effects are typically less dramatic and do less to capture the public imagination.

There is something about prisons that is damaging. But what is it?

Even the most humanely designed prisons have negative effects on the people living and working inside. And that is the deep truth we are still seeking to understand and the Stanford Prison Experiment effectively illustrates.

• Mental health
• Criminal justice
• Prison reform
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• Waterboarding
• Solitary confinement
• Prison guards

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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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AQA A-Level Psychology - ZIMBARDO'S STANFORD PRISON EXPERIMENT (1971) [Social Influence Topic]

Subject: Psychology

Age range: 16+

Resource type: Lesson (complete)

Last updated

26 September 2024

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This fully editable lesson is designed for the AQA A-Level Specification (June 2019), focusing on Zimbardo’s Stanford Prison Experiment (1971) and its exploration of conformity to social roles. This resource provides students with an in-depth analysis of the procedures, findings, and critical evaluation of Zimbardo’s study, emphasizing ethical considerations and real-world applications.

Key Features:

• Comprehensive Lesson Slides: Covers Zimbardo’s Stanford Prison Experiment, including participant recruitment, procedures, and the behaviour of both prisoners and guards. Key findings and conclusions are explored in detail.
• Interactive Video Activities: Features a video question sheet to accompany a video on Zimbardo’s research, prompting students to analyze the recruitment, treatment, and behaviour of participants during the study.
• Assessment Materials: Includes practice exam questions such as outlining Zimbardo’s research and discussing two limitations of the study, with model answers provided to support exam preparation.
• Critical Evaluation: Students engage in evaluating the ethical issues, sample bias, and dispositional influences present in Zimbardo’s research, exploring the extent to which the study’s findings can be generalized to real-life scenarios like prison environments.

This lesson resource is well-suited for classroom instruction or independent study, providing a comprehensive approach to understanding social influence and the power of situational factors on human behaviour.

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Get this resource as part of a bundle and save up to 25%

A bundle is a package of resources grouped together to teach a particular topic, or a series of lessons, in one place.

AQA A-Level Psychology: SOCIAL INFLUENCE Topic (10 Full Lessons)

This comprehensive bundle is designed in line with the latest AQA A-Level Specification (published June 2019), though its content and activities are suitable for use across various specifications. It provides everything you need to teach the Social Influence topic in an engaging and structured way, offering 10 complete lessons, each with interactive activities and assessment materials. Included Lessons: 1. Types and Explanations of Conformity – Understanding different forms of conformity and their explanations. 2. Asch’s Research (1951, 1955) – Exploring Asch’s famous experiments on conformity. 3. Zimbardo’s Research (1971) – Examining the Stanford Prison Experiment and the influence of social roles. 4. Milgram’s Research (1963) – Investigating obedience to authority through Milgram’s groundbreaking experiments. 5. Milgram’s Situational Variables – How situational factors impact obedience. 6. Social-Psychological Factors – Delving into factors like legitimacy of authority and the agentic state. 7. Dispositional Explanations: The Authoritarian Personality – Understanding obedience through personality traits. 8. Resistance to Social Influence – Exploring the factors that help individuals resist pressures to conform or obey. 9. Minority Influence – How minority groups can bring about social change. 10. Social Influence and Social Change – The processes that lead to large-scale societal shifts. Each lesson comes as a fully-editable PowerPoint, with carefully designed activities that encourage critical thinking, class discussion, and application of research. For more details, please see individual lesson descriptions. If you have any questions, need assistance with resources, or would like to provide feedback, feel free to reach out at [email protected]. Reviews and feedback are highly appreciated!

CONFORMITY LESSONS BUNDLE [AQA A-Level Psychology – Social Influence]

This mini-bundle has been created in line with the latest AQA A-Level Specification (published June 2019), though the content and activities are adaptable for use with other specifications. It includes three fully editable lessons, each designed to engage students with the key concepts of conformity through interactive tasks and research-based discussions. Lessons Included: * Types and Explanations of Conformity – A comprehensive exploration of compliance, identification, and internalization. * Asch’s Research (1951, 1955) – Delve into the classic experiments on group pressure and conformity. * Zimbardo’s Research: The Stanford Prison Experiment (1971) – An in-depth look at how social roles influence behavior. Each lesson comes with detailed PowerPoints and accompanying activities to encourage critical thinking, discussion, and exam preparation. For inquiries, feedback, or if you encounter any issues accessing the resources, feel free to contact me at [email protected]. Reviews and feedback are always appreciated. Please see individual lesson descriptions for a full breakdown of content.

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The Stanford Prison Experiment: Meet the Filmmaker

• TV & FILM

Director Kyle Patrick Alvarez, actors Ezra Miller and Michael Angarano, and Dr. Philip Zimbardo discuss The Stanford Prison Experiment. Based on the real-life research of Dr. Zimbardo (Billy Crudup)—the movie tells the story of the infamous 1971 psychology experiment that took place in a mock prison in the Stanford lab.

Director Kyle Patrick Alvarez, actors Ezra Miller and Michael Angarano, and Dr. Philip Zimbardo discuss their new film.

Information

• Creator Apple
• Years Active 2K
• Copyright ℗ & © 2015 Apple Inc.
• Show Website The Stanford Prison Experiment: Meet the Filmmaker

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