prison experiment in stanford

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Stanford Prison Experiment

• Quiet Rage: The Stanford Prison Experiment

About the Stanford Prison Experiment

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

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

Samples from the Collection

Photographs

Video Recordings

Transcripts

Stanford Prison Experiment: Zimbardo’s Famous Study

Saul McLeod, PhD

Editor-in-Chief for Simply Psychology

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

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

Learn about our Editorial Process

Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

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

On This Page:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Asserting Authority

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

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

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

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

Physical Punishment

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

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

Asserting Independence

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

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

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

Putting Down the Rebellion

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

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

Special Privileges

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

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

Consequences of the Rebellion

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

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

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

Prisoner #8612

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

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

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

A Visit from Parents

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

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

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

Catholic Priest

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

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

Prisoner #819

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

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

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

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

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

Back to Reality

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

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

An End to the Experiment

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Critical Evaluation

Ecological validity.

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

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

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

Demand characteristics

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

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

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

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

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

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

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

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

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

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

Sample bias

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

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

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

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

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

Zimbardo’s conclusion may be wrong

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

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

Contributions to psychology

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

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

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

Contribution to prison policy

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

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

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

The authors argue psychologists should reengage to:

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

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

Evidence for situational factors

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

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

Evidence for an interactionist approach

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

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

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

Ethical Issues

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

Protection of Participants

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

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

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

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

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

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

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

Withdrawal 

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

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

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

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

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

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

Discussion Questions

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

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

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

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

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

Frequently Asked Questions

What happened to prisoner 8612 after the experiment.

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

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

Why did Zimbardo not stop the experiment?

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

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

What happened to the guards in the Stanford Prison Experiment?

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

What did Zimbardo want to find out?

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

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

What were the results of the Stanford Prison Experiment?

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

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

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

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

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

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

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

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

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

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

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

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

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

Further Information

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

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

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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.

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

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

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

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

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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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How the Stanford Prison Experiment Worked

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The Takeaways

Zimbardo realized that rather than a neutral scenario, he created a prison much like real prisons, where corrupt and cruel behavior didn't occur in a vacuum, but flowed from the rules and principles of the institution to the people who carried out those principles. The behavior of the guards and prisoners wasn't dictated by some inherent internal trait, but by the situation they were in. The theory that external circumstances are the primary drivers of human behavior is known as situationist theory . Zimbardo didn't form the theory, but his experiment and later writings helped popularize it.

Experimental ethics are also an issue to consider. The Stanford Human Subjects Review Committee and Zimbardo's superiors approved the experiment — another layer of authority complicit in the experiment's outcome (it's like situationist "Inception") — but experimental ethics are more rigorous today. A modern institutional review board would likely never approve such an experiment without major modifications. Zimbardo has said that he feels the initial experiment was ethical (all the participants understood what they'd signed up for and consented), but that he suffered an ethical lapse when he allowed it to continue beyond the first emotional breakdown of a prisoner [source: Stanford Prison Experiment ].

The idea that humans have an inherent tendency toward abuse of authority and submission to authority is not ruled out by the experiment, however. The Stanford Prison Experiment is closely related to another psychological experiment that's as infamous: Stanley Milgram's obedience to authority experiment . In fact, Zimbardo and Milgram were high school classmates and colleagues at Yale University. In the obedience experiment, volunteers were directed to press buttons delivering increasingly powerful, and eventually fake lethal shocks to another person at the direction of a researcher. A large percentage of volunteers went along with the researcher's demands. However, like the Stanford Prison Experiment, the ethics, methodology and conclusions of Milgram's experiment have been called into question recently . And both experiments influenced changes in the regulation and ethical guidelines of studies with human subjects [sources: Zimbardo et al. , Defiesta ].

Zimbardo's conclusion was that we are not so much inherently "evil," but that we will commit heinous acts if encouraged to do so by systems that enable or encourage them. He took his results to the U.S. House of Representatives shortly after the experiment ended, testifying before a subcommittee on prison reform. His primary argument was that given the power institutions have to dictate the behavior of the people within them, it's necessary to reform those institutions to avoid those abuses. He suggested better training and pay for guards, better protection for prisoners' human rights , and specific training programs that could include role-playing scenarios to help guards learn to deal humanely with prisoners (and weed out the most sadistic among guards) [source: House of Representatives ]. The 2003 scandal surrounding prisoner treatment at the Iraqi prison Abu Ghraib, which mirrored the actions of Zimbardo's guards in disturbing ways, suggests that the experiment is not a relic of the past but still relevant to the way people are treated in modern civilian and military prisons.

Zimbardo's testimony also reflected his belief that researchers should not remain impartial observers, but should engage in social and political ways to act on the discoveries they make and seek ways to improve the world [source: Zimbardo et al. ].

Remember that part about Zimbardo's experiment lacking a control group? In 2002, the BBC broadcasted a similar experiment, one that conformed with modern ethics and removed many of the initial biases, such as dehumanizing the prisoners and giving the guards implements of authority. In many ways it could be seen as a control group for the Stanford Prison Experiment. The outcome? The prisoners stuck together, and the guards became disorganized. Like the Stanford Prison Experiment, this one ended early, because a group of participants planned to take over the prison, and the researchers anticipated violence [source: Reicher & Haslam ].

Author's Note: How the Stanford Prison Experiment Worked

Much of the appeal of the Stanford Prison Experiment, aside from the dark, voyeuristic thrill of learning how the subjects acted, is how easily it lets you insert yourself into the narrative Zimbardo created. What kind of guard would you be? How would you react when another guard did something sadistic? How would you react as a prisoner? Would you organize your fellow prisoners, or work against them to gain favor with the guards? Or maybe you envision yourself in Zimbardo's position, pulling the strings in your scenario. How would you have changed the conditions to alter the subjects' behavior? Could you redesign the experiment to be more ethical?

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• California Released Thousands of Prisoners Early — Guess How That Turned Out

More Great Links

• The Milgram Experiment
• Carnahan, Thomas et al. "Revisiting the Stanford Prison Experiment: Could Participant Self-Selection Have Led to the Cruelty?" Personality and Social Psychology Bulletin. Vol. 33, issue 5. May 1, 2007. (June 22, 2017) http://journals.sagepub.com/doi/abs/10.1177/0146167206292689
• Defiesta, Nick. "When Psychologists 'Go Wrong.'" Yale Daily News. Sept. 28, 2011. (July 14, 2017) http://yaledailynews.com/blog/2011/09/28/when-psychologists-go-wrong/
• Haney, Craig et al. "Interpersonal Dynamics in a Simulated Prison." International Journal of Criminology and Penology. 1973. (June 10, 2017) http://pdf.prisonexp.org/ijcp1973.pdf
• House of Representatives. "Hearings Before Subcommittee No. 3 of the Committee on the Judiciary, House of Representatives, Ninety-Second Congress, First Session on Corrections Part 2, Prisons, Prison Reform, and Prisoner Rights: California." Oct. 25, 1971. (June 12, 2017) http://pdf.prisonexp.org/congress.pdf
• Konnikova, Maria. "The Real Lesson of the Stanford Prison Experiment." The New Yorker. June 12, 2015. (June 12, 2017) http://www.newyorker.com/science/maria-konnikova/the-real-lesson-of-the-stanford-prison-experiment
• Ratnesar, Romesh. "The Menace Within." Stanford Magazine. July/August 2011. (July 14, 2017) https://alumni.stanford.edu/get/page/magazine/article/?article_id=40741
• Reicher, Stephen & S. Alexander Haslam. "Rethinking the psychology of tyranny: The BBC prison study." British Journal of Social Psychology. 2006. (June 12, 2017) http://www.bbcprisonstudy.org/pdfs/BJSP(2006)Tyrannny.pdf
• Sedacca, Matthew. "The Man Who Played With Absolute Power." Feb. 16, 2017. (July 6, 2017) http://nautil.us/issue/45/power/the-man-who-played-with-absolute-power
• Stanford Prison Experiment. "The Story." (June 12, 2017) http://www.prisonexp.org/the-story
• Zimbardo, Philip G. "A Situationist Perspective on the Psychlogy of Evil." "The Social Psychology of Good and Evil," Gilford Press. 2004. (June 12, 2017) http://pdf.prisonexp.org/evil.pdf
• Zimbardo, Philip G. et al. "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 Assoc. 2000. (June 12, 2017) http://pdf.prisonexp.org/blass.pdf

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

How The Stanford Prison Experiment Revealed The Darkest Depths Of Human Psychology

Conducted by philip zimbardo in august 1971, the stanford prison experiment revealed how ordinary people could quickly adopt abusive behaviors when given authority and power..

In October 2004, U.S. Army Staff Sergeant Ivan “Chip” Frederick was facing some hard time. He had been one of the accused in the notorious torture scandal that erupted in March of that year from Iraq’s Abu Ghraib prison, and his court-martial saw disturbing details aired about prisoner abuse, sleep deprivation, and sexual humiliation.

One of the witnesses that Frederick called to defend him — and arguably one of the reasons he only got eight years for his crimes — was Stanford psychologist Philip Zimbardo, who argued that Frederick’s actions weren’t necessarily a reflection on his character, but were instead a reaction to the environment that commanding officers had allowed to develop in Abu Ghraib.

Zimbardo explained that, given the right set of circumstances, almost anyone could be induced to do some of the things of which Frederick stood accused: beat naked prisoners, defile their religious items, and force them to masturbate with hoods over their heads.

PrisonExp.org Prisoners with bags forced over their heads await their “parole hearing,” their release from the Stanford Prison Experiment upon its conclusion.

Frederick’s actions, Zimbardo argued, were the predictable outcome of his assignment, rather than the isolated acts of a “bad apple,” which had been the Army’s approach to shifting blame onto certain individuals.

At the court-martial, Zimbardo was able to speak with a certain expertise on the subject of prisoner abuse because he had once participated in it himself.

For six days, between August 14 and 20, 1971, he had been the “warden” of a mock prison in the basement of Stanford University’s Jordan Hall.

In an effort to better understand what drove the interactions of prisoners and their guards — funded by a grant from the U.S. Navy and Marine Corps — Zimbardo devised a psychological experiment that saw two-dozen otherwise normal young men randomly assigned the role of either prisoner or guard for what was intended to be a two-week role-playing exercise.

PrisonExp.org A naked prisoner stands behind bars during the Stanford prison experiment.

Under Philip Zimbardo’s watch, the Stanford prison experiment turned into a struggle between suffering prisoners and the manipulative, sadistic guards who enjoyed torturing them.

The results were written up and widely circulated, making Zimbardo famous throughout his profession, and revealing something very disturbing about how little it sometimes takes to turn people into monsters.

How The Stanford Prison Experiment Got Started

A decade before the Stanford prison experiment, Yale psychologist Stanley Milgram carried out an experiment in 1961 to test the willingness of some people to deliver electric shocks to strangers.

The Milgram experiment , as it came to be known, revealed that it’s upsettingly easy to talk some young men into shocking another person to death (which they were led to believe they may have done, although no subjects were actually harmed).

PrisonExp.org A guard escorts a blindfolded prisoner through the makeshift Stanford prison.

This experiment pointed the way forward for more research into situational behavior and the premise that we are only as good or as bad as our surroundings will let us be. Philip Zimbardo was not present for the Milgram experiment, but he had been a psychology student at Yale until 1960, and by 1971, he was ready to take Milgram’s work one step further at Stanford.

That’s when the U.S. Office of Naval Research commissioned him to study the psychology of confinement and power as it exists between guards and their inmates. Zimbardo accepted the grant and got to work on the Stanford prison experiment right away.

The site chosen for the experiment was in the basement of Jordan Hall, on the Stanford campus. There, Zimbardo set up four “prison cells” using interior partitions, as well as a “warden’s office” and various common areas for the guards to use for recreation. There was also a small broom closet, which will become relevant later on.

Zimbardo recruited subjects for his test by placing an ad in the Stanford Daily , asking for “male students” who were needed “to participate in a psychological study of prison life.” The ad promised compensation of $15 a day (equivalent to roughly $90 in 2017).

When his subjects applied for the experiment, Zimbardo carefully screened them to weed out potential bad apples. Anyone with a criminal record, however minor, was declined participation, as were applicants with histories of psychological aberrations and behavioral problems.

In the end, Philip Zimbardo was left with 24 healthy college-age men who had no detectable tendencies toward violence or other negative behaviors. Shortly before the Stanford prison experiment began, the subjects were randomly assigned to either the prisoner group or the guard group.

The night before the experiment, Zimbardo held an orientation meeting for his 12 guards. He gave them firm instructions regarding their duties and limitations: Guards would be organized into three eight-hour shifts to provide round-the-clock supervision of the inmates.

They were given military-surplus khakis, mirrored sunglasses, and wooden batons as a symbol of authority. The guards were all told not to hit or otherwise physically abuse the prisoners, though they were told they’d have wide discretion in how they treated the 12 prisoners under their watch.

PrisonExp.org Stanford Police handcuff prisoner #8612 before transporting him to the prison.

The next day, members of the Palo Alto Police Department arrived at the designated prisoners’ homes and took them into custody. The 12 men were booked into the county jail and searched, fingerprinted, and had their mugshots taken.

At length, they were transported to the Stanford campus and escorted into the basement, where the guards were waiting for them. Prisoners were given ill-fitting smocks and told to wear large stocking caps. Each had a short length of chain looped around his ankle to drive home their status as prisoners. They were assigned three to a cell and given a lecture about the rules.

Every angle had been worked out to make the prisoners feel subordinate to the guards, including the large numbers sewn onto their smocks; guards had been told to address inmates only by these numbers, rather than allowing them the dignity of names.

By the end of the Stanford prison experiment’s first day, both sides had fully internalized the rules and begun acting toward each other as if their power dynamic had existed all along.

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Revolt And Uproar

PrisonExp.org Prisoners are made to face the wall as a guard watches over them.

Though both sides had internalized their roles and some inmates seemed to chafe at the boredom and the arbitrary nature of their guards’ commands, the first day of the Stanford prison experiment had passed by more or less uneventfully.

Prisoners would sometimes be pulled out of their cells and searched, even though they couldn’t possibly have had contraband that early in the experiment. The guards were generally rude and condescending. They often demanded that prisoners repeat their numbers to drive home their lowly status. Menial tasks were assigned, and penalties, such as being ordered to hold stress positions for extended periods, were being imposed.

By that first night, the guards had decided to punish less-compliant prisoners by taking away their mattresses, forcing them to sleep on the cold floor. They also disrupted the inmates’ sleep by being noisy in their common area, which was adjacent to the cells.

By noon on day two, prisoner #8612 had started showing the signs of a breakdown. He started screaming and raging, and Zimbardo himself had to come in to control the situation. The prisoner refused to calm down, and so the decision was made to release him from the study for his own sake.

This took the form of a “parole hearing,” accompanied by an extended stint in the broom closet, which was doing duty as a solitary confinement area. The release process was intended to be long and arduous, in order to further the impression that the prison was an all-powerful institution where inmates were helpless.

Bear in mind that this was all a voluntary exercise, and that — in principle, at least — everybody was free to go whenever they wanted to.

PrisonExp.org As a form of punishment during the Stanford experiment, a prisoner is made to scrub a toilet.

While prisoner #8612 was being processed out, the other 11 prisoners were in an uproar. Arbitrary and cruel treatment by the guards had already provoked inmates to refuse to obey orders or to leave their cells. They refused to answer to their numbers when called.

Inmates in one cell barricaded themselves in by propping a mattress against the door. By that evening, things were bad enough that some guards, who were free to go home after their shift, volunteered to stay overtime and suppress the revolt.

After the clinical staff observing the experiment went home, the guards left on duty hit prisoners with blasts from a fire extinguisher and transferred them to the other cells to increase crowding. The empty cell was reserved for “good” inmates who hadn’t participated in the uprising. Perceived ringleaders, on the other hand, were shut up in solitary for hours.

Prisoners in the regular cells were refused leave to use the bathroom and were instead given buckets to relieve themselves in. The buckets were then left unemptied in the cell all night long. The next day, guards forced the prisoners to stand in stress positions without their clothes on for hours at a time.

Too Dangerous To Continue

PrisonExp.org Guards begin a strip search of a prisoner.

By day three of the Stanford prison experiment, things were rapidly coming unglued. According to Zimbardo, roughly one-third of the guards spontaneously developed signs of genuine sadism, consistently inventing new forms of punishment and egging the other guards on as these punishments were inflicted on the helpless inmates.

Guards and inmates both — who had, remember, been randomly assigned their roles only a few days prior — began identifying with their side and acting collectively. After a few days, most of the inmates had joined together in a hunger strike to protest their conditions, while the guards were pulling extra shifts for free and becoming increasingly paranoid.

When a rumor got started about prisoner #8612 coming back with a small army of supporters to stage a jailbreak, none other than Zimbardo ordered the basement prison to be disassembled and moved upstairs while he waited alone in the basement for the attackers. He later said his plan, if the man had actually shown up, was to tell him the experiment had been terminated and to send him home.

PrisonExp.org Philip Zimbardo waits alone in the basement of Jordan Hall for the rumored attack on the experiment led by a prisoner who became unhinged and was released early.

By this point, Philip Zimbardo had become fully immersed in the experiment himself.

As he later admitted, it was never going to be possible for him to maintain objectivity in his role as prison administrator, and so he found himself bound up in the fantasy world he had created for his test subjects. Zimbardo found himself becoming morbidly curious about where the experiment was going and what new developments each day would bring.

By day four, when certain inmates were becoming suicidal and apparently losing their grip on reality, Zimbardo thought the situation interesting enough to bring in his girlfriend — herself a psychology graduate student — to have a look at what was going on. The woman, 26-year-old Christina Maslach, was appalled by what she saw and said so.

In the past, whenever a new person was brought in from the outside — such as prisoner #416, who replaced #8612 — they went through a period of normalization.

But #416’s objections to his treatment got him locked up in solitary, where the guards would torment him by pounding on the door with their hands in shifts. By the time he got out of the solitary confinement closet, prisoner #416 had been sufficiently broken as to accept the routine of prison life as normal.

Maslach, on the other hand, couldn’t be locked up or broken in that way, and her fresh perspective on what was going on shocked her boyfriend into seeing his nightmare through her eyes. So it was that on day six of the Stanford prison experiment, Dr. Zimbardo announced its termination — much to the dismay of his guards, who had grown to quite like the power they had been abusing all week.

Afterward, everybody was still unhinged enough that it took a full day to “parole” the remaining inmates, though — again — the experiment was over and they weren’t being paid anymore; they could have just left.

The Legacy Of The Stanford Prison Experiment Today

PrisonExp.org A guard wears his issued uniform while holding his baton during the Stanford prison experiment.

The Stanford prison experiment became a classic study of human psychology and power dynamics. Perhaps the most stunning findings were that the people who took part in the study almost instantly internalized their roles so completely that they seem to have forgotten that they even had lives outside of the prison.

Guards acted with exceptional brutality, as if they would never have to answer for their actions, while prisoners put up with appalling abuses of their human rights without, for the most part, demanding to be let go.

Perhaps even more disturbing, many researchers and graduate students had passed through the basement during the Stanford prison experiment, observed the conditions of the men’s confinement, and said nothing about it. Later on, Philip Zimbardo estimated that perhaps 50 people had seen what was going on in his basement prison, and his girlfriend was the only one who objected.

Zimbardo’s findings immediately found relevance when, just two weeks after the Stanford prison experiment ended, inmates in the notorious San Quentin and Attica prisons rose up in violent revolts that were strikingly similar to what had happened on day two of the experiment at Stanford.

Zimbardo was called to testify before the House Judiciary Committee about prison conditions and their effect on human behavior. Zimbardo’s contention had always been that external conditions, rather than an individual’s personality, determine how people react under stress.

Partly as a result of Philip Zimbardo’s research, the decision was made in the United States to separate juvenile and adult offenders as well as to impose stricter controls and protections for prison inmates who, for instance, wish to file a lawsuit challenging their conditions.

But the Stanford prison experiment, like the earlier Milgram experiment, had implications that go far beyond prison management.

PrisonExp.org A prisoner sits blindfolded inside the prison.

In both experiments, seemingly normal, mentally stable human beings were induced — with virtually no coercion and only a little encouragement — to commit horrific crimes against other people. In both cases, the decisions made by individuals would have been unthinkable had they been acting on their own, and strongly suggest that reactions can be conditioned by the local environment when the decisions are made.

This casts a gloomy light on the distinctions that society makes between criminals and law-abiding citizens, as well as suggesting some disturbing possibilities in regards to the perpetrators of humanity’s greatest crimes.

Nazi death squad members, for example, famously argued that they bore no personal malice, but were only following orders; if they had been ordered to do something other than shooting thousands of civilians, they would have.

The postwar trials of these men did not accept this as a defense, but Philip Zimbardo’s research suggests it might have been an excellent excuse; worse, it could be the excuse that any normal person uses when some dictator or other autocrat issues them with khakis and eyeshades, gives them a baton, and tells them to control the prisoners in their cells — as seems to have happened at Abu Ghraib, and probably many other places that didn’t make the news.

After this look at the Stanford Prison Experiment, read up on the most evil science experiments ever conducted . Then, discover what some of the cruelest Nazi research and experimentation contributed to medical science .

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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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Inside The Stanford Prison Experiment Today In History with The Retrospectors

Listen on Apple Podcasts Requires subscription and macOS 11.4 or higher

The Stanford Prison Experiment, created by Philip Zimbardo, began on 14th August, 1971. 24 male college students volunteered to be assigned roles as either ‘guard’ or ‘prisoner’ in a mock jail: the ‘prisoners’ were ‘arrested’ by real cops outside their family homes and marched down to a Police Station before being transferred to their imitation incarceration. Once inside, they were stripped, deloused, and given smocks and ID numbers; while guards were outfitted with khaki uniforms, mirrored sunglasses, and batons, establishing a stark power divide. The guards quickly embraced their roles, with some becoming cruel and abusive. They enforced strict, often humiliating regimens on the prisoners, such as roll calls and physical exercises, to instill a sense of powerlessness. But the guards were not aware they were also subjects of the study… In this episode, Arion, Rebecca and Olly interrogate the selection process and context that belies the study’s impact; consider the distress supposedly experienced by the participants; and ask if this controversial experiment should now be scrubbed from the textbooks… Further Reading: • ‘The Stanford Prison Experiment: Philip Zimbardo defends his most famous work’ (Vox, 2018): https://www.vox.com/science-and-health/2018/6/28/17509470/stanford-prison-experiment-zimbardo-interview • ‘Philip Zimbardo Thinks We All Can Be Evil’ (The New York Times, 2015): https://www.nytimes.com/2015/07/19/magazine/philip-zimbardo-thinks-we-all-can-be-evil.html • ‘The Stanford Prison Experiment Was One of the Most Disturbing Studies Ever’ (Weird History, 2020): https://www.youtube.com/watch?v=IRR7CwdHxUE Thanks so much for supporting the show! We massively appreciate it. The Retrospectors are Olly Mann, Rebecca Messina & Arion McNicoll, with Matt Hill. Edit producer: Ollie Peart Theme Music: Pass The Peas. Announcer: Bob Ravelli. Graphic Design: Terry Saunders. Copyright: Rethink Audio / Olly Mann 2024.

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Philip Zimbardo (Biography + Experiments)

Who Is Philip Zimbardo?

Philip Zimbardo is a prominent Italian-American psychologist, author, and retired professor. He is best known for his work in the Stanford Prison Experiment—widely considered one of the most impactful and controversial social psychology experiments in history. The experiment has been the subject of conversations, classes, and even movies for years. 

Philip Zimbardo Short Biography

Zimbardo was born in New York City in 1933. Zimbardo believes his interest in human behavior was sparked during his childhood. He often experienced prejudice and discrimination in those early years due to his Italian descent and poor financial background.

Despite his humble beginnings, Zimbardo completed his bachelor’s degree at Brooklyn College in 1954, with a triple major in psychology, sociology, and anthropology. He earned his Master’s degree (1955) and doctoral degree (1959) at Yale University. From 1959-2003, Zimbardo taught at a number of prestigious universities including Yale, New York University, Columbia, and Stanford. 

What is The Stanford Prison Experiment?

The Stanford Prison Experiment was a study conducted in 1971 that examined how situational forces and perceived power affect human psychology. It focused primarily on the interactions and interpersonal relationships between prisoners and prison guards in a prison-like environment. The experiment was funded by the United States Office of Naval Research. The research team was led by Philip Zimbardo and included Craig Haney, W. Curtis Banks, and David Jaffe.

The experiment was conducted in the basement of the psychology building at Stanford University. After an ad was put out in the Palo Alto City newspaper, college students from all over the United States and Canada volunteered to participate. Those selected were assigned roles as either prisoners or prison guards.  A mock prison with three small prison cells was constructed for the experiment.

As the study progressed, the relationship between the “prisoners” and the “prison guards” eroded drastically. Some reports suggest the prisoners were subjected to psychological torture. Several prisoners had to be released from the experiment when they were unable to cope with the deteriorating conditions. Although the study was designed to run for up to two weeks, it was brought to a premature end after just six days.

Stanford Prison Experiment Method

Twenty-four college males were recruited for the experiment. They were told the study involved a two-week prison simulation and they would be paid $15 per day. The subjects were primarily white, middle class, and had no criminal background. The researchers also took care to select participants who had no history of medical or psychological issues.

The subjects were randomly assigned as either prisoners or guards by flipping a coin. There were 9 guards (with 3 possible substitutes) and 9 prisoners (also with 3 possible substitutes). David Jaffe, who was an undergraduate research assistant at the time, served as the warden of the prison. Zimbardo played the role of superintendent.

The prison was intentionally constructed without windows or clocks. Each prison cell measured 6 x 9 feet, contained three cots, and held three prisoners. A long corridor (boarded up at each end) served as the "yard" for the prisoners. A small closet was used as the "hole" for solitary confinement.

The prisoners wore nylon stocking caps, a loose-fitting dress with an identification number, a heavy chain around their right ankle, rubber sandals, and no underclothes. Being forced to wear a dress immediately led to some prisoners having to sit more like a woman than a man. The prison attire was specially chosen to emasculate, humiliate, and oppress the inmates. The nylon caps symbolized their hair being shaved off and minimized their individuality.

Guards were given identical khaki uniforms, mirrored sunglasses to prevent eye-contact, a whistle, and a baton to symbolize their power. Their clothing gave them a sense of authority and anonymity. They were also given much more space than the prisoners as well as rest periods, personal comforts, and areas for relaxation. The guards received no formal training on prison management.

Rules of the Study

Before the study began, the guards were told not to harm the prisoners physically, or limit their food and water. However, they were allowed to induce fear or boredom in the prisoners, as well as take away their privacy. Rather than address the prisoners by name, the guards were instructed to call them by their identification numbers. Zimbardo designed the experiment to (1) give the guards the feeling of complete control and (2) rob the prisoners of their sense of reality, time, space, and self.

On the first day of the experiment, the Palo Alto police department assisted Zimbardo by arresting the prisoners at their homes and taking them through the entire booking process. The prisoners were charged with crimes, given their Miranda warning, handcuffed, fingerprinted, and photographed. The sudden, unexpected arrest left many of the prisoners in mild shock. After booking they were blindfolded and placed in a holding cell at the police station until pickup.

When the prisoners arrived at the mock prison they were strip searched and deloused. The purpose was to humiliate them and ensure no pests were introduced into the prison. Three guards worked at a time in eight hour shifts. The prisoners were forced to remain on site as they needed to be locked up for the majority of the experiment.

Results of the Stanford Prison Experiment

While the first day of the study ended without any major incident, the second day began with a riot. Some of the prisoners decided to block the cell doors with their beds. In a show of defiance, they discarded their caps and tore off their prison numbers. They also hurled insults at the guards.

With three guards finding it difficult to manage nine prisoners, the guards from the other shifts agreed to help end the riot. They eventually used a fire extinguisher to douse the prisoners in ice cold carbon dioxide and forced them away from the doors. Once inside the cells, the guards stripped the prisoners and took away their beds. The ringleaders were forced into solitary confinement.

Upon realizing that they were outnumbered on each shift, the guards decided to attack the prisoners psychologically in order to strengthen their control over them. Prisoners who did not actively participate in the revolt were placed in a “privilege cell” that offered clothing, better food, beds, and the opportunity to wash and brush their teeth. However, the prisoners in the privileged cell were soon replaced with prisoners who were in the "bad" cells. This tactic was used to confuse the prisoners and break their unity.

As a part of their psychological attack, the guards instructed the prisoners to memorize and repeat their assigned numbers throughout the day. This was usually done during the numerous prisoner counts. The guards also forced the prisoners to refer to each other by number. This tactic helped to deindividualize the prisoners and bolstered the idea that their numbers were their new identity.

Approximately 35 hours into the experiment, one prisoner—identified as #8612—began to scream, curse, and lash out in rage. The researchers were eventually forced to released him from the study as he showed signs of depression, disorganized thinking, and uncontrollable crying.

Increasing Cruelty

The researchers noted that as the experiment went on, the guards treated the prisoners with increasing cruelty. The guards developed a series of methods for punishing the prisoners which included:

• Doing tedious, meaningless work
• Refusing requests to go to the bathroom
• Not being allowed to empty their sanitation buckets (which were kept in the cells)
• Solitary confinement
• Sleep deprivation
• Cleaning toilets with their hands
• Cursing each other publicly
• Wearing a paper bag over their heads
• Laughing, singing or smiling on command
• Doing pushups, sometimes with a guard's foot on their backs
• Picking thorns out of their blankets (the blankets were dragged through thorn bushes by the guards)

All In on the Experiment 

On day three, the guards became concerned after hearing a rumor that released prisoner #8612 planned to return with friends to break the other inmates out of prison. The researchers, who were now completely caught up in the experiment themselves, took steps to thwart the attack by moving the prison out of the basement to another floor. Zimbardo also planned to intercept the attackers and tell them that the study had ended. However, the attackers never showed up and the prison was moved back to the basement.

The longer the experiment went on, the more absorbed the participants and the researchers became. One guard who felt sorry for the prisoners and wanted to help them was encouraged by “warden” David Jaffe to get more involved and get tougher. By day five, three additional prisoners had to be released from the study because they showed signs of anxiety. A fifth inmate developed a psychosomatic rash over his entire body after his "parole" was rejected by a mock parole board. He too was released from the experiment.

Solitary Confinement

When prisoner #416—a newly admitted participant—refused to eat, he was subjected to increased abuse from the guards. When the guards were unable to force him to eat, #416 was put in solitary confinement. He was only allowed to return to his cell after seven of the other eight prisoners agreed to give up their blankets.

While the prisoners had shown solidarity during the first rebellion on day two, they now regarded #416 as just a trouble-maker. The unity among the inmates had completely deteriorated. In many cases they obeyed the guards blindly, even when the instructions were unjust. It appeared as if all the participants had forgotten that this was just an experiment.

Why Did the Stanford Prison Experiment End Early?

The study was brought to an abrupt end on day six. Christina Maslach—a graduate student in psychology and Zimbardo’s girlfriend at the time—arrived on site to conduct a series of interviews with the subjects. When she saw the condition the prisoners were in, her immediate reaction was one of shock and disgust. The Stanford Prison Experiment was discontinued later that day after Maslach strongly questioned the morality of the study.

Conclusions from the Stanford Prison Experiment

The study highlighted how certain social contexts can significantly influence or transform human behavior. Although all the subjects had been carefully screened across a variety of physical and personality measures before the study, it did not take long for them to act in a manner neither they nor the researchers expected. Some guards became increasingly cruel and sadistic in their efforts to harass the prisoners. The other guards gave off an air of indifference and did nothing to stop the mistreatment.

The prisoners also showed drastic changes in behavior due to the psychological trauma they experienced. Some inmates begged to be released from prison shortly after the experiment started and most of them were willing to obey even the most unreasonable commands from the guards. Zimbardo believed that the participants’ change in behavior was because they had begun to internalize their assigned roles . As the experiment went on, the guards increasingly believed they had the authority to do anything they wanted within the confines of the prison and the prisoners increasingly thought of themselves as less than important than the guards.

The goal of the Stanford Prison Experiment was to show how prison-like environments could influence the people who pass through them. It clearly demonstrated how insane situations can lead to insane behaviors from normal people. It also highlighted the power of perceived authority, the pressure individuals face to conform to their assigned social group , and how people may respond to cognitive dissonance .

The researchers believed the behavior of the students greatly mirrored the behavioral patterns found in actual prisons. Several insights from the experiment were adopted by the United States government to improve the management of correctional facilities across the nation.

Criticism and Limitations of The Stanford Prison Experiment

Over the years, an increasing number of people have expressed concerns about the ethics of the Stanford Prison Experiment. Many critics were appalled that young men were subjected to psychological torture for days in the name of social psychology. The extremely unsanitary condition of the mock prison also raised concerns about the physical health of the inmates. The fact that the guards were able to find ways to harass the prisoners without being supervised by the research team was another safety issue that was not adequately addressed before or during the study.

Several critics argued that the experiment lacked scientific rigor and produced no real results. They believe the behavior of the students was influenced by the fact that they knew they were being observed. Rather than a behavioral change occurring naturally, some opponents point to the fact that Zimbardo explicitly instructed the guards to use psychological tactics. After the study, one guard commented that he behaved the way he did because he wanted the researchers to get good data they could work with.

Later reports even show that the guards were instructed to "act tough."  

Zimbardo himself admitted that the study did not measure up to the standards of a scientific experiment as it did not have a control group, a comparison group, or other defined variables. Rather than a rigorous scientific experiment, Zimbardo asserted that his study was a valid demonstration of what can happen to human behavior in certain social contexts.

Replications of Stanford Prison Experiment 

A number of researchers have tried to replicate the Stanford Prison Experiment in the decades that followed. But although they copied Zimbardo’s methodology, they were not able to replicate his findings. However, real-world events at Abu Ghraib prison brought the Stanford Prison Experiment back to public attention in 2004. The sadistic acts committed by several United States military personnel at the Iraqi prison almost perfectly mirrored Zimbardo's 1971 study.   

Zimbardo’s Other Interests, Contributions, and Awards

After the Stanford Prison Experiment, Zimbardo delved into other areas of social psychology that interested him. This included in-depth research on topics such as the psychology of shyness, evil, violence, terrorism, heroism, madness, persuasion, hypnosis, dissonance, and time perspective. He has written several books on his findings and some of his research papers are considered required reading for a number of psychology courses today. In 2012, he was awarded the American Psychological Foundation Gold Medal for Lifetime Achievement in the Science of Psychology.

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. Retrieved from https://www.gvsu.edu/cms4/asset/F51281F0-00AF-E25A-5BF632E8D4A243C7/stanford_prison_experiment.pdf

O’Toole, K. (1997, January 8). The stanford prison experiment: Still powerful after all these years. Retrieved from https://news.stanford.edu/pr/97/970108prisonexp.html

Philip. G. Zimbardo. (2016, September 8). Retrieved from http://zimbardo.socialpsychology.org/

The Story: An Overview of the Experiment. (n.d.). Retrieved from https://www.prisonexp.org/

Zimbardo, P., Haney, C., Banks, W. C. & Jaffe, D. (1971). The stanford prison experiment: A simulation study of the psychology of imprisonment. Retrieved from https://web.stanford.edu/dept/spec_coll/uarch/exhibits/Narration.pdf

Related posts:

• Stanford Prison Experiment
• Outgroup Bias (Definition + Examples)
• Ivan Pavlov (Biography + Experiments)
• Albert Bandura (Biography + Experiments)
• Human Experimentation List (in Psychology)

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The Stanford Prison Experiment

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

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• Philip Zimbardo
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• 67 Metascore
• 4 wins & 3 nominations

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• Daniel Culp …

• Peter Mitchell …

• Dr. Philip Zimbardo

• Dr. Christina Maslach

• Christopher Archer

• Anthony Carroll

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• Prisoner 416

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Did you know

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

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

Christopher Archer : So why do you hate me?

Daniel Culp : Because I know what you can become.

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

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Understanding the Milgram Experiment in Psychology

A closer look at Milgram's controversial studies of obedience

Isabelle Adam (CC BY-NC-ND 2.0) via Flickr

Factors That Influence Obedience

• Ethical Concerns
• Replications

How far do you think people would go to obey an authority figure? Would they refuse to obey if the order went against their values or social expectations? Those questions were at the heart of an infamous and controversial study known as the Milgram obedience experiments.

Yale University  psychologist   Stanley Milgram  conducted these experiments during the 1960s. They explored the effects of authority on obedience. In the experiments, an authority figure ordered participants to deliver what they believed were dangerous electrical shocks to another person. These results suggested that people are highly influenced by authority and highly obedient . More recent investigations cast doubt on some of the implications of Milgram's findings and even the results and procedures themselves. Despite its problems, the study has, without question, made a significant impact on psychology .

At a Glance

Milgram's experiments posed the question: Would people obey orders, even if they believed doing so would harm another person? Milgram's findings suggested the answer was yes, they would. The experiments have long been controversial, both because of the startling findings and the ethical problems with the research. More recently, experts have re-examined the studies, suggesting that participants were often coerced into obeying and that at least some participants recognized that the other person was just pretending to be shocked. Such findings call into question the study's validity and authenticity, but some replications suggest that people are surprisingly prone to obeying authority.

History of the Milgram Experiments

Milgram started his experiments in 1961, shortly after the trial of the World War II criminal Adolf Eichmann had begun. Eichmann’s defense that he was merely following instructions when he ordered the deaths of millions of Jews roused Milgram’s interest.

In his 1974 book "Obedience to Authority," Milgram posed the question, "Could it be that Eichmann and his million accomplices in the Holocaust were just following orders? Could we call them all accomplices?"

Procedure in the Milgram Experiment

The participants in the most famous variation of the Milgram experiment were 40 men recruited using newspaper ads. In exchange for their participation, each person was paid $4.50.

Milgram developed an intimidating shock generator, with shock levels starting at 15 volts and increasing in 15-volt increments all the way up to 450 volts. The many switches were labeled with terms including "slight shock," "moderate shock," and "danger: severe shock." The final three switches were labeled simply with an ominous "XXX."

Each participant took the role of a "teacher" who would then deliver a shock to the "student" in a neighboring room whenever an incorrect answer was given. While participants believed that they were delivering real shocks to the student, the “student” was a confederate in the experiment who was only pretending to be shocked.

As the experiment progressed, the participant would hear the learner plead to be released or even complain about a heart condition. Once they reached the 300-volt level, the learner would bang on the wall and demand to be released.

Beyond this point, the learner became completely silent and refused to answer any more questions. The experimenter then instructed the participant to treat this silence as an incorrect response and deliver a further shock.

Most participants asked the experimenter whether they should continue. The experimenter then responded with a series of commands to prod the participant along:

• "Please continue."
• "The experiment requires that you continue."
• "It is absolutely essential that you continue."
• "You have no other choice; you must go on."

Results of the Milgram Experiment

In the Milgram experiment, obedience was measured by the level of shock that the participant was willing to deliver. While many of the subjects became extremely agitated, distraught, and angry at the experimenter, they nevertheless continued to follow orders all the way to the end.

Milgram's results showed that 65% of the participants in the study delivered the maximum shocks. Of the 40 participants in the study, 26 delivered the maximum shocks, while 14 stopped before reaching the highest levels.

Why did so many of the participants in this experiment perform a seemingly brutal act when instructed by an authority figure? According to Milgram, there are some situational factors that can explain such high levels of obedience:

• The physical presence of an authority figure dramatically increased compliance .
• The fact that Yale (a trusted and authoritative academic institution) sponsored the study led many participants to believe that the experiment must be safe.
• The selection of teacher and learner status seemed random.
• Participants assumed that the experimenter was a competent expert.
• The shocks were said to be painful, not dangerous.

Later experiments conducted by Milgram indicated that the presence of rebellious peers dramatically reduced obedience levels. When other people refused to go along with the experimenter's orders, 36 out of 40 participants refused to deliver the maximum shocks.

More recent work by researchers suggests that while people do tend to obey authority figures, the process is not necessarily as cut-and-dried as Milgram depicted it.

In a 2012 essay published in PLoS Biology , researchers suggested that the degree to which people are willing to obey the questionable orders of an authority figure depends largely on two key factors:

• How much the individual agrees with the orders
• How much they identify with the person giving the orders

While it is clear that people are often far more susceptible to influence, persuasion , and obedience than they would often like to be, they are far from mindless machines just taking orders. 

Another study that analyzed Milgram's results concluded that eight factors influenced the likelihood that people would progress up to the 450-volt shock:

• The experimenter's directiveness
• Legitimacy and consistency
• Group pressure to disobey
• Indirectness of proximity
• Intimacy of the relation between the teacher and learner
• Distance between the teacher and learner

Ethical Concerns in the Milgram Experiment

Milgram's experiments have long been the source of considerable criticism and controversy. From the get-go, the ethics of his experiments were highly dubious. Participants were subjected to significant psychological and emotional distress.

Some of the major ethical issues in the experiment were related to:

• The use of deception
• The lack of protection for the participants who were involved
• Pressure from the experimenter to continue even after asking to stop, interfering with participants' right to withdraw

Due to concerns about the amount of anxiety experienced by many of the participants, everyone was supposedly debriefed at the end of the experiment. The researchers reported that they explained the procedures and the use of deception.

Critics of the study have argued that many of the participants were still confused about the exact nature of the experiment, and recent findings suggest that many participants were not debriefed at all.

Replications of the Milgram Experiment

While Milgram’s research raised serious ethical questions about the use of human subjects in psychology experiments , his results have also been consistently replicated in further experiments. One review further research on obedience and found that Milgram’s findings hold true in other experiments. In one study, researchers conducted a study designed to replicate Milgram's classic obedience experiment. The researchers made several alterations to Milgram's experiment.

• The maximum shock level was 150 volts as opposed to the original 450 volts.
• Participants were also carefully screened to eliminate those who might experience adverse reactions to the experiment.

The results of the new experiment revealed that participants obeyed at roughly the same rate that they did when Milgram conducted his original study more than 40 years ago.

Some psychologists suggested that in spite of the changes made in the replication, the study still had merit and could be used to further explore some of the situational factors that also influenced the results of Milgram's study. But other psychologists suggested that the replication was too dissimilar to Milgram's original study to draw any meaningful comparisons.

One study examined people's beliefs about how they would do compared to the participants in Milgram's experiments. They found that most people believed they would stop sooner than the average participants. These findings applied to both those who had never heard of Milgram's experiments and those who were familiar with them. In fact, those who knew about Milgram's experiments actually believed that they would stop even sooner than other people.

Another novel replication involved recruiting participants in pairs and having them take turns acting as either an 'agent' or 'victim.' Agents then received orders to shock the victim. The results suggest that only around 3.3% disobeyed the experimenter's orders.

Recent Criticisms and New Findings

Psychologist Gina Perry suggests that much of what we think we know about Milgram's famous experiments is only part of the story. While researching an article on the topic, she stumbled across hundreds of audiotapes found in Yale archives that documented numerous variations of Milgram's shock experiments.

Participants Were Often Coerced

While Milgram's reports of his process report methodical and uniform procedures, the audiotapes reveal something different. During the experimental sessions, the experimenters often went off-script and coerced the subjects into continuing the shocks.

"The slavish obedience to authority we have come to associate with Milgram’s experiments comes to sound much more like bullying and coercion when you listen to these recordings," Perry suggested in an article for Discover Magazine .

Few Participants Were Really Debriefed

Milgram suggested that the subjects were "de-hoaxed" after the experiments. He claimed he later surveyed the participants and found that 84% were glad to have participated, while only 1% regretted their involvement.

However, Perry's findings revealed that of the 700 or so people who took part in different variations of his studies between 1961 and 1962, very few were truly debriefed.

A true debriefing would have involved explaining that the shocks weren't real and that the other person was not injured. Instead, Milgram's sessions were mainly focused on calming the subjects down before sending them on their way.

Many participants left the experiment in a state of considerable distress. While the truth was revealed to some months or even years later, many were simply never told a thing.

Variations Led to Differing Results

Another problem is that the version of the study presented by Milgram and the one that's most often retold does not tell the whole story. The statistic that 65% of people obeyed orders applied only to one variation of the experiment, in which 26 out of 40 subjects obeyed.

In other variations, far fewer people were willing to follow the experimenters' orders, and in some versions of the study, not a single participant obeyed.

Participants Guessed the Learner Was Faking

Perry even tracked down some of the people who took part in the experiments, as well as Milgram's research assistants. What she discovered is that many of his subjects had deduced what Milgram's intent was and knew that the "learner" was merely pretending.

Such findings cast Milgram's results in a new light. It suggests that not only did Milgram intentionally engage in some hefty misdirection to obtain the results he wanted but that many of his participants were simply playing along.

An analysis of an unpublished study by Milgram's assistant, Taketo Murata, found that participants who believed they were really delivering a shock were less likely to obey, while those who did not believe they were actually inflicting pain were more willing to obey. In other words, the perception of pain increased defiance, while skepticism of pain increased obedience.

A review of Milgram's research materials suggests that the experiments exerted more pressure to obey than the original results suggested. Other variations of the experiment revealed much lower rates of obedience, and many of the participants actually altered their behavior when they guessed the true nature of the experiment.

Impact of the Milgram Experiment

Since there is no way to truly replicate the experiment due to its serious ethical and moral problems, determining whether Milgram's experiment really tells us anything about the power of obedience is impossible to determine.

So why does Milgram's experiment maintain such a powerful hold on our imaginations, even decades after the fact? Perry believes that despite all its ethical issues and the problem of never truly being able to replicate Milgram's procedures, the study has taken on the role of what she calls a "powerful parable."

Milgram's work might not hold the answers to what makes people obey or even the degree to which they truly obey. It has, however, inspired other researchers to explore what makes people follow orders and, perhaps more importantly, what leads them to question authority.

Recent findings undermine the scientific validity of the study. Milgram's work is also not truly replicable due to its ethical problems. However, the study has led to additional research on how situational factors can affect obedience to authority.

Milgram’s experiment has become a classic in psychology , demonstrating the dangers of obedience. The research suggests that situational variables have a stronger sway than personality factors in determining whether people will obey an authority figure. However, other psychologists argue that both external and internal factors heavily influence obedience, such as personal beliefs and overall temperament.

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