experiment prison guards and inmates

Stanford Prison Experiment: Zimbardo’s Famous Study

Saul McLeod, PhD

Editor-in-Chief for Simply Psychology

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

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

Learn about our Editorial Process

Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

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

On This Page:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Asserting Authority

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

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

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

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

Physical Punishment

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

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

Asserting Independence

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

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

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

Putting Down the Rebellion

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

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

Special Privileges

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

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

Consequences of the Rebellion

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

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

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

Prisoner #8612

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

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

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

A Visit from Parents

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

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

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

Catholic Priest

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

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

Prisoner #819

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

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

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

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

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

Back to Reality

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

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

An End to the Experiment

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Critical Evaluation

Ecological validity.

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

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

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

Demand characteristics

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

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

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

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

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

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

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

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

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

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

Sample bias

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

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

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

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

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

Zimbardo’s conclusion may be wrong

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

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

Contributions to psychology

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

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

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

Contribution to prison policy

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

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

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

The authors argue psychologists should reengage to:

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

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

Evidence for situational factors

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

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

Evidence for an interactionist approach

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

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

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

Ethical Issues

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

Protection of Participants

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

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

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

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

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

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

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

Withdrawal 

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

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

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

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

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

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

Discussion Questions

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

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

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

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

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

Frequently Asked Questions

What happened to prisoner 8612 after the experiment.

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

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

Why did Zimbardo not stop the experiment?

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

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

What happened to the guards in the Stanford Prison Experiment?

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

What did Zimbardo want to find out?

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

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

What were the results of the Stanford Prison Experiment?

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

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

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

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

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

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

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

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

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

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

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

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

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

Further Information

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

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The Stanford Prison Experiment

• Participants
• Setting and Procedure

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

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

Purpose of the Stanford Prison Experiment

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

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

Participants in the Stanford Prison Experiment

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

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

Setting and Procedures

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

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

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

Results of the Stanford Prison Experiment

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

It was noted that:

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

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

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

Impact of the Zimbardo Prison Experiment

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

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

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

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

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

Criticisms of the Stanford Prison Experiment

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

Ethical Issues

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

Why was Zimbardo's experiment unethical?

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

Lack of Generalizability

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

Lack of Realism

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

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

Recent Criticisms

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

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

Among the issues described:

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

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

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

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

Stanford University. About the Stanford Prison Experiment .

Stanford Prison Experiment. 2. Setting up .

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

Ratnesar R. The menace within . Stanford Magazine.

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

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

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

American Psychological Association. Ecological validity .

Blum B. The lifespan of a lie . Medium .

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

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

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

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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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The Real Lesson of the Stanford Prison Experiment

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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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

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

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

by Brian Resnick

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

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

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

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

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

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

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

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

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

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

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

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

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

Brian Resnick

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

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

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

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

So does that not invalidate the conclusion?

Philip Zimbardo

Not at all!

And why not?

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

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

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

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

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

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

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

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

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

And I reject that.

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

Zero? How can you say zero?

Okay, I can’t say.

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

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

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

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

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

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

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

Brian, I’m gonna stop you.

Can I finish the question?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

You don’t want to talk about him.

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

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

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

You don’t assume good faith on their part?

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

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

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

The view that situation can make a difference?

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

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

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

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

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

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

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

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

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

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

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

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

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

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Chapter 4: Understanding and Influencing Others

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Social Roles

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

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

Social Norms

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

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

Zimbardo’s Stanford Prison Experiment

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

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

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

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

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

Suggested Reading

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

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

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How the Stanford Prison Experiment Worked

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A Deeper Look at the Stanford Prison Experiment

Zimbardo has written extensively about the experiment, filling in major details about what happened. There were nine prisoners and nine active guards. The remaining three participants on each side were on standby in case they were needed. The guards operated in shifts, and the prisoners were always present. The guards were initially reluctant in their roles, the prisoners defiant. But on the second day, the prisoners united: They locked themselves in their cells, insulted the guards and ripped the prisoner numbers off their uniforms, rebelling against the guards' authority. The guards used the incoming shift and the standby guards as reinforcements to put down the rebellion, stripping the prisoners naked and taking away their beds [source: Zimbardo ]. This incident also marked the introduction of physical punishments like pushups (often with a guard placing his foot on a prisoner's back).

The guards even instituted a "privilege" cell, one with beds and good meals for the three best-behaved prisoners, and used it to turn the prisoners against each other. At the apex of the guards' brutality, they tried to keep a prisoner in solitary confinement , which was literally a tiny closet barely large enough to fit a person, for an entire night, only relenting when one of the researchers stepped in. And during the night shift, when the guards thought they were not being observed, their torment of the prisoners turned to more intense physical punishment, waking the prisoners throughout the night and forcing them to perform vaguely erotic acts (such as standing very close to each other).

But the guards were not all equally brutal. There was a "ringleader" guard, nicknamed John Wayne, who seemed especially vicious, as well as guards who did the prisoners favors and did not punish them severely. However, the "good" guards never objected to or complained about the behavior of the sadistic guards. The brutal guard, whose real name is Dave Eshelman, has claimed in interviews that he was acting the part he thought the researchers wanted to see. But he has noted that pretending didn't absolve him of his cruelty, since his actions obviously caused misery [source: Ratnesar ].

By the end of the experiment, the prisoners exhibited no solidarity, while the guards and even Zimbardo had grown to see the prisoners as a threat that needed to be subdued for the safety of the guards and the integrity of the prison [source: Stanford Prison Experiment ]. Everyone involved became so deeply immersed in the experiment's role-playing scenario that at one point the prisoners were offered "parole." That is, they could be released if they would forfeit any money they'd earned for participating. In a parole hearing, most of the prisoners said they would forfeit their money, and the parole board members (secretaries, students and the prison consultant) said they had to consider if they would allow parole for those prisoners who accepted the offer. The board sent the prisoners back to their cells, and the prisoners complied, even though they had the ability to walk away from the experiment (giving up the $15 per day) at any time [source: Haney et al. ].

The five prisoners who were released (no guards left the experiment) experienced irrational thinking, unstable emotions and severe anxiety. One even broke out in a psychosomatic rash. In fact, the prisoners either had breakdowns, faked breakdowns so they could leave or simply became "zombies," going along with whatever the guards made them do with little or no emotional reaction.

But on day six, Zimbardo called off the experiment, realizing it had quickly become problematic.

Zimbardo and his team went to astonishing lengths to make their prison seem realistic. During a visiting hour, parents and friends were subjected to arbitrary prison rules, such as being forced to wait to see an "inmate" and having a limited amount of time to speak to him. Also, a former prison chaplain who was brought in to speak to the prisoners suggested they get legal counsel if they wanted to get out of the prison. When some parents asked for a lawyer, a lawyer came in and played along as if it were a real prison. And when the first prisoner to emotionally break down asked to leave, he was convinced to stay when the researchers' prison consultant manipulated and browbeat him. When he went back to the other prisoners, he told them he'd learned they really couldn't leave.

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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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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Talk of the Nation

Prison psychology and the stanford prison experiment.

A look at prison behavior: In 1971, volunteer students acted so badly during a study of the psychology of prisoners and guards, the study had to be cut short. Guest: Philip Zimbardo *Psychology professor at Stanford University *Conducted Stanford Prison Experiment in 1971

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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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Watch CBS News

John Manard, inmate whose escape from Kansas prison in a dog crate inspired a movie, dies at age 45

Updated on: August 30, 2024 / 7:21 AM EDT / CBS/AP

An inmate whose escape from a Kansas prison hidden in a dog crate became the subject of a book and TV movie has died behind bars.

John Manard, who was 45, died Sunday at the La Palma Correctional Facility, a private prison in Eloy, Arizona, according to the Kansas Department of Corrections . His cause of death is pending the result of an autopsy, department spokesperson Jennifer King said.

Manard was serving a life sentence for a suburban Kansas City killing at a prison in Lansing, Kansas, when he met Toby Young, a married mother of two who worked helping prisoners train animals for adoption. They struck up a romantic relationship.

On Feb. 12, 2006, Young, then 47, hid Manard, then 27, in a crate and helped him escape.

Prison officials said she took advantage of the trust she gained while running the program to drive Manard out of the prison. A guard who recognized Young did not thoroughly search the van.

Young and Manard were captured 12 days after the escape in east Tennessee on Interstate 75 between Knoxville and Chattanooga, about 90 miles south of a remote cabin they had been sharing.

According to The  Kansas City Star , authorities searched the cabin and found a parakeet, sex toys, a guitar and sheet music to the movie "O Brother, Where Art Thou?"

Young, whose husband filed for divorce after her arrest, was sentenced in state court for her role in breaking Manard out. She also pleaded guilty in federal court to giving him a gun. She was freed in 2008 and wrote about what happened in the book, "Living With Conviction."

"John is finally free. But I am crushed," Young, who has since remarried and goes by Toby Dorr, said in a Facebook post Wednesday. "I pray you have at last found the peace you were searching for, John."

The escape story also was featured on "Dateline" and is the inspiration behind the Lifetime movie, "Jailbreak Lovers."

In a March 2006 letter to a Kansas City television station, Manard said he and Young "have a fairytale love the size of infinity."

In a letter to the Kansas City Star , Manard called himself a "17-year-old child" and said the fatal carjacking that he was serving a life sentence for was a huge mistake.

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ISIS prisoners killed after slashing guards, seizing hostages in Russian jail

Four knife-wielding prisoners claiming to be Islamic State group militants launched a deadly attack in a penal colony in southern Russia on Friday before being killed and their hostages released, officials said.

The attack left four people dead, while the four hostage-taking prisoners were “neutralized” by snipers, Russian officials said.

The attackers initially seized eight penal colony employees and four fellow inmates, according to Russia's Federal Penitentiary Service.

"The criminals inflicted stab wounds of varying severity on four employees, three of whom died. Another four who resisted were hospitalized, one of whom died in hospital," it said in a statement.

All four convicts taken hostage were injured, the service added.

The incident unfolded in IK-19, a prison based in the town of Surovikino in the southern Volgograd region. It is designated a “harsh regime” penal colony with capacity to hold up to 1,241 male prisoners.

News sites with security connections published the names of up to four alleged attackers, identifying them as citizens of Uzbekistan and Tajikistan. There was no official confirmation of these reports.

President Vladimir Putin said he has been informed about the “situation,” and will be meeting with his security officials to discuss it.

“The criminals were eliminated,” the region’s governor, Andrei Bocharov, said in a statement on the Telegram messaging app. “Unfortunately, there are people who died from the actions of criminals.”

Earlier, Bocharov said four injured employees of the colony had been hospitalized and the surrounding civilian population was in no danger.

“Every person on our territory is obliged to respect and comply with the laws of Russia," he added. "We will not allow anyone to try to incite ethnic hatred.”

Russia, whose defense and security agencies are heavily focused on its war in Ukraine , has seen a recent upsurge in Islamist militant attacks.

In June, a bloody ISIS-linked prison uprising took place in the southern region of Rostov , where special forces shot dead six inmates who had taken hostages.

Later that month, at least 20 people were killed in shooting attacks in two cities in Dagestan , a mainly Muslim region of southern Russia.

In March, ISIS claimed responsibility for an attack in which gunmen raided the Crocus City concert hall near Moscow , sprayed the audience with automatic weapons fire and set fire to the building, killing more than 140 people.

Yuliya Talmazan is a reporter for NBC News Digital, based in London.

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INVESTIGATION AND ANALYSIS OF ORGANIZED CRIME

Arrests Shed Light on Abuse of Women in Guatemala’s Prisons

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Guatemalan authorities have made multiple busts of prison guards involved in sexual exploitation schemes that victimize women behind bars, showing rare government action on a problem that often remains hidden, and highlighting the challenge of battling corruption in the penitentiary system. 

Police detained eight prison guards on August 16, alleging they sexually exploited female prisoners in the departments of Suchitepéquez, El Progreso, Baja Verapaz, and Guatemala. The guards charged male inmates money for transporting women to other prisons and forcing them to perform sexual acts, prisons director Sergio Vela told local media. 

This case follows the arrest in March of nine guards who allegedly trafficked young girls into prisons, where they were sexually abused by inmates. Some of the male prisoners belonged to the Barrio 18 gang, and after abusing the girls they then made them carry out crimes outside the prison, according to reporting. The case was part of a broader investigation by a branch of the Attorney General’s Office focused on human trafficking (Unidad contra Estructuras Criminales y Casos Especiales de la Fiscalía contra la Trata de Personas). Another 2023 investigation found three other guards in Mazatenango, a mixed-gender prison, charged between $40 and $200 per girl. 

SEE ALSO: The Timebomb That Exploded Twice: Behind the Massacres in Honduras’ Women’s Prison

Guatemala’s overcrowded prisons are hotspots of criminal activity , and corruption within prison staff is rampant. Both the Barrio 18 and the Mara Salvatrucha (MS13), who victimize women in trafficking schemes, have considerable power behind bars. 

The number of women in prisons is rising, putting more women in conditions that make them vulnerable to sexual exploitation and abuse. In 2015, women represented 9.1% of the total prison population in Guatemala. By 2023, that number had increased to 12.1%. Most female inmates are aged between 18 and 35, said Andrea Barrios, who runs Colectivo Artesanas, a non-governmental organization that advocates for the rights of women in prison in Guatemala.

Since taking office, the government of President Bernardo Areválo has vowed to curb criminal activity and corruption inside prisons, and authorities have launched a number of raids in key penitenciaries and removed dozens of guards from their posts. But they face an uphill struggle.  “The problem that we have is a penitentiary system that’s out of control, in which many of the guards are involved [in corruption]”, said Francisco Jiménez, Guatemala’s Interior Minister to Prensa Libre.

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These recent cases in Guatemala’s prisons could be the tip of the iceberg of incidents of sexual exploitation enabled by prison guards and systemic corruption. 

Barrios, who has daily contact with female inmates in Guatemala, says this kind of sexual exploitation is common, but rarely investigated and prosecuted. 

After the recent arrests, the female victims were moved to other prisons. “That’s punishing them because it is moving them away from where they know, and their families,” said Barrios. None of the prison guards have been charged with human trafficking, and instead were accused of neglecting their duties and put under house arrest.

Years of abandonment, overcrowding, corruption, and a lack of professionalization in the penitentiary system have made the oversight of prisons nearly impossible, said Corinne Dedik, an analyst at the Guatemala-based think tank Centro de Investigaciones Económicas Nacionales (CIEN).

SEE ALSO: Why Are There More Women in Mexican Prisons for Organized Crime?

Systematic corruption within prison authorities is necessary for these types of human trafficking and exploitation schemes to operate. No one can leave and enter without the participation of prison guards, including those in charge of female-only areas, as well as prison directors, explained Barrios.  

A lack of career development or advancement also brings problems. “There is no career path in Guatemala’s penitentiary system. Everyone gets their training, and they stay at that level because there’s no chance to move up,” said Dedik. This opens the door to criminal incentives, she explained.

Most prisons in the country house both sexes, with women living in female-only zones in male-dominated prisons. The porous separation between the men and women inside creates opportunities for exploitation, according to a 2023 report by the Inter-American Commission on Human Rights (IACHR).

“Women in prison have many needs that the state doesn’t meet and their families can only provide limited support,” said Barrios. Products , like shampoo, soap, and sanitary towels are scarce, and families often have to provide them for inmates. A large percentage of women in prisons are also single mothers and the main breadwinners in their families. “Those in power take advantage of the women’s needs and profit from it, and that’s where the authorities are responsible,” said Barrios. The control of criminal groups like the Barrio 18 in prisons allows them to further corrupt and control officials to allow them to bring in women and girls.  

SEE ALSO: One Prison, Two Gangs

The government faces a difficult problem in tackling systemic corruption.  “The penitentiary system stagnated in the 60s and 70s, but today the world out there is different,” said Dedik. “These types of situations can only be improved using sustainable methods, which would require fundamental, deep reform.” 

Barrios welcomed the latest arrests in sexual exploitation cases in prisons, but said that she would love to see prevention measures put in place, such as better vetting of prison authorities and surveillance of visitation areas. Featured image: Police detain prison guards involved in a sexual exploitation scheme in Guatemala. Credit: Guatemala Attorney General’s Office.

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The Stanford Prison Experiment

Now a major film, to be released this week, decades after the “experiment.”.

Posted July 15, 2015

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By Philip Zimbardo

Forty-four years ago, I conducted a research experiment that could have been the bane of my existence. 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 lead me to study why, in difficult situations, some people heroically step forward to help others – oftentimes complete strangers - while others stand by and watch. The psychological time warp experienced by participants of the SPE – not knowing if it was day or night or what day it was - lead to my research in our individual time perspectives and how these affect our lives. 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 lead 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 the experiment had to be shut down after only six days.

Challenging the Truth

There seems 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, and also in the dominating influence of our 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 of 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 spokesmen. 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 1000 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 my defendant, Chip Frederick, as a really Good Apple corrupted by being forced to function 12-hours every night for many months in the worse barrel imaginable. My situation-based testimony to the military Court Martial hearings helped reduce the severity of his sentence.

“The Stanford Prison Experiment” Film

On July 15, The Stanford Prison Experiment premiers in New York City. The Los Angeles premier – as well as nationwide release is scheduled for July 17. The film stars 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. In January, The Stanford Prison Experiment received two awards at the Sundance Film Festival: best screenwriting and best science feature.

What is special about the The Stanford Prison Experiment movie is the way it 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 guys soon slip into doing extraordinarily bad things to other guys, who are actually just like them except for a random coin flip. Other healthy guys 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-objective observer are dominated by power and insensitivity to prisoner suffering in the new role of Prison Superintendent. The six-day process of transformations in the original experiment is crunched down to 2 hours, but the magic of the movie’s acting, directing and editing psychologically expands that time frame’s full force. We feel the power of social situations dominating personalities; as viewers are encouraged to ponder:

What kind of Guard would I be? What kind of Prisoner? What kind of Superintendent? And would I have blown the whistle to end this drama sooner, or not?

My hope is that this movie can do what my writings about this special research into human nature have not been fully able to do. Perhaps now viewing and reliving this adventure will enable the general public to better appreciate the value of what “research shows” about mind, behavior and the pervasive power of situational forces.

Here is a recent Huffington Post interview that includes the movie trailer:​

http://www.huffingtonpost.com/entry/stanford-prison-experiment-creator-… ?

Visit the official Stanford Prison Experiment website to learn more about the experiment that inspired the film: www. prisonexp.org

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) http://heroicimagination.org/ teaches ordinary people how to stand up, speak out and take effective actions in challenging situations in their lives.

Working and learning together, we can create a new generation of ordinary everyday heroes who will do extra-ordinary deeds of daily heroism in their families, schools, businesses, and communities.

Phil Zimbardo

Learn more about yourself and how to cope with stress and anxiety , visit www.discoveraetas.com .

For in depth information about how your life is affected by the mental time zones that you live in, please check out our website: www.timeperspectivetherapy.org , and our books: The Time Cure at www.timecure.com and The Time Paradox at www.thetimeparadox.com

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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Snipers kill knife-wielding inmates claiming to be IS fighters who seized guards at Russian jail

The National Guard Service said the inmates were "neutralised" and all hostages freed, though the number was not specified, the reports said.

Friday 23 August 2024 17:05, UK

Russian snipers have killed four armed prisoners who seized guards at a jail and declared allegiance to the Islamic State, according to local media reports.

Earlier, the Russian website Mash showed a video of at least two attackers, with one declaring they were "mujahideen" and saying they had taken over the prison.

Four uniformed officials could be seen in pools of blood - three of them motionless. Another was sitting upright in a doorway with a knife held to his neck.

Other videos showed four men pacing about a prison yard where a bloodied prison staff member was being held hostage.

One of the prisoners appeared to have an improvised explosive vest while the others were carrying knives and hammers.

Before the inmates were shot state news agency Tass said four victims had been taken to hospital, with two of them in serious condition.

Unconfirmed reports on the Telegram messaging app said one or two people had died.

The violence occurred on Friday at a penal colony, believed to be IK-19 in Surovikino, southwestern Russia .

"During a session of a disciplinary commission, convicts took staff of the penal institution as hostages," said a prison service statement.

Read more from Sky News: The horror of life as an ISIS sex slave Warning of IS resurgence - as Sky speaks to terrorists' families IS group behind Moscow attack sought recruits in Britain

Russian news sites published the names of four alleged attackers and said they were from Uzbekistan and Tajikistan, but there has been no official confirmation.

President Vladimir Putin was later recorded at a security council meeting asking leaders for an assessment of the situation.

The prison involved can hold more than 1,200 male inmates and is classed as a "harsh regime" penal colony.

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This year has seen a number of Islamist militant attacks in Russia.

The worst was in March when more than 140 people died after gunmen attacked a concert hall near Moscow and set the building on fire.

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Special forces also shot dead six people involved in an IS -linked prison uprising in June in the southern Rostov region.

At least 20 were killed in the same month in shootings in Dagestan , a predominately Muslim region also located in southern Russia.

Inmates take hostage at Russian prison, reportedly claim support for Islamic State

MOSCOW (AP) — Inmates at a Russian prison took guards as hostages and claimed allegiance to the Islamic State group, leaving at least four people injured, Russian news reports said Friday.

Details of the violence at the prison in Surovkino, 860 kilometers (535 miles) southeast of Moscow, were sparse and did not specify the number of hostage-takers or people seized.

Russian news site Meduza posted a video that it said was from the scene, showing men wielding knives inside and in a prison yard and several men in what appeared to be guard uniforms lying in blood on the ground.

State news agency Tass said four victims were taken to a local hospital and two of them were in serious condition. Unconfirmed reports on Telegram messaging channels said one or two people died.

In the video, the alleged attackers claimed support for IS and for the suspects arrested in the March terrorist attack on a Moscow concert hall that left 145 people dead. An IS affiliate claimed responsibility for the attack, in which gunmen killed patrons waiting for a popular music group to perform and set the building on fire.

Tass said court records showed that four of the hostage-takers were from former Soviet Central Asian countries; all the concert hall attack suspects are from Tajikistan.

Authorities closed off the road leading to the prison and sent in officers to try to end the violence.

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