Stanford Prison Experiment: Zimbardo’s Famous Study

Saul Mcleod, PhD

Editor-in-Chief for Simply Psychology

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

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

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Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

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

On This Page:

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

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

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

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

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

zimbardo guards

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.

zimbardo prison

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.

prisoner counts

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.

prisoner 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.


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

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

prison experiment ethical issues

Cara Lustik is a fact-checker and copywriter.

prison experiment ethical issues

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

Introduction, archival sources.

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

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

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

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

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

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

The Stanford Prison Experiment .

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

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

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

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

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

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Rosemary K.M. Sword and Philip Zimbardo Ph.D.

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

The experiment generated important research into unexplored territories..

Posted August 16, 2021 | Reviewed by Tyler Woods

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

Phil Zimbardo

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

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

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

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

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

The Experiment in a Nutshell

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

Challenging the Truth

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

Denial and Finger Pointing

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

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

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

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

“The Stanford Prison Experiment” Film

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

child is sitting jeans

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

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

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

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

Heroic Imagination

Phil Zimbardo

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

Rosemary K.M. Sword and Philip Zimbardo Ph.D.

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

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What the Stanford Prison Experiment Taught Us

Guards with a blindfolded prisoner, still from the Stanford Prison Experiment conducted by Phillip Zimbardo

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

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

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

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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.


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

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

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

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

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

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

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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


Video Recordings


The Stanford Prison Experiment was massively influential. We just learned it was a fraud.

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

by Brian Resnick

Rorschach test 

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

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

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

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

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

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

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

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

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

Many classic findings in psychology have been reevaluated recently

prison experiment ethical issues

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Textbooks need to catch up

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

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

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

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

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

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

prison experiment ethical issues

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

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

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

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

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

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

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

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

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

Further reading: Psychology’s “replication crisis”

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

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'The Stanford Prison Experiment'

By  Jacqueline Thomsen

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The Stanford University prison experiment was abruptly ended 44 years ago after treatment of pseudoprisoners by pseudoguards, both played by students, escalated too far for the researchers to tolerate.

The study has since found a hallmark place in Psych 101 and AP Psychology courses as books and documentaries on the topic have been created. And this summer, a feature film on the experiment was released, cementing an already well-established place in popular culture.

The Stanford Prison Experiment has received positive reviews from critics , echoing reactions to the film’s first screening at Sundance Film Festival last year. But the timing for a movie revolving around the ethics of psychology could not be more relevant, as reports on the involvement of top officials at the American Psychological Association being complicit in the torture of others by U.S. agencies emerge.

During the experiment in the summer of 1971, 24 young men were assigned the role of either a prisoner or a guard and quickly adapted to their roles, maintaining the appearance of a 24-hour prison in the basement of a hall on Stanford's campus. The guards, who worked in eight-hour shifts, took advantage of their power, and the prisoners rebelled within 36 hours of the start of the experiment, but each individual soon forgot that they were subjects in an experiment and not people in a prison.

The movie is no different. The first half of the movie is completely dedicated to describing the setup of the study and the first 48 hours. Tensions run high, prisoners attempt to escape and the psychologists running the show find themselves more deeply intertwined in the process than they had anticipated.

Philip Zimbardo, the Stanford University psychology professor who oversaw the original experiment, said he has been trying to make the film a reality for 35 years. Today at 82, an emeritus professor of psychology at the university, he said he closely collaborated with the screenwriter and director of the movie to make the film as accurate as possible.

Zimbardo said that as he was writing his 2007 book on the experiment, The Lucifer Effect , he would send chapters to the screenwriter, Tim Talbott, to help develop the script. He also said all dialogue between the prisoners and the guards was taken straight from the recordings of the experiment, which was filmed in its entirety.

Only one scene in the film didn’t sit well with Zimbardo. At one point in the film, Zimbardo's character is approached by another Stanford professor, who asks what the independent variable in the experiment was. Zimbardo said the scene came across as if he didn’t know what the experiment was about, and he asked for it to be removed, but it was too late in production to do so.

“Of all of the things in the movie, this is probably the most negative because it looks like I didn’t know the answer,” Zimbardo said.

The experiment itself has come under fire over the years. Peter Gray, a research professor at Boston College, decided not to include the Stanford prison experiment in his psychology textbook because he didn’t believe the study, which was never published in a peer-reviewed journal, was a legitimate experiment and that it was essentially fabricated by Zimbardo.

Gray, whose book is now in its sixth edition, called the study “an embarrassment to the field of psychology.”

“He got a bunch of college kids to pretend they’re prisoners and another group to pretend they’re guards, told them what they’re supposed to do and then they did it,” he said.

Gray has not seen the movie, but said so many people have asked him about it that he may watch it in the future.

And a paper co-authored by Sam McFarland, now an emeritus professor of psychology at Western Kentucky University, found that there could have been bias in the selection of those who participated in the experiment because the word “prison” was included in the advertisement for subjects. The film opens with the writing and printing of the advertisement.

McFarland said that individuals could have been encouraged or deterred from joining a “psychological study of prison life” by the word “prison.” His paper found that individuals who responded positively to the original wording were more likely to be aggressive and narcissistic and less empathetic than those who would have signed up for only a psychological study with no mention of prison life in the wording.

Zimbardo stood by his experiment, saying that it’s still “the most powerful demonstration in psychology,” even if other psychologists didn’t believe it was a true experiment.

As for the ethics of the experiment, Zimbardo said he believed the experiment was ethical before it began but unethical in hindsight because he and the others involved had no idea the experiment would escalate to the point of abuse that it did.

The movie ends with Zimbardo’s character and some of the prisoners and guards describing how they felt throughout the experiment and some of its findings. There is also a disclaimer, saying that none of the subjects suffered any long-term or negative effects from their involvement in the study.

And as the ethics of the experiment are once again discussed with the release of the film, so is the current state of ethics in psychology. Three top officials of the American Psychological Association stepped down last month after a 542-page report described how members of the organization who worked with the Department of Defense were complicit in the torture of individuals by federal agencies.

Zimbardo, a former president of the APA who was traveling to the association’s annual conference at the time of this interview, said he hoped the film would help contribute to a conversation about ethics by psychologists.

“It raises those basic questions -- these people who are Ph.D.s in psychology, who understand human nature, whose job it is to develop a set of ethical guidelines to help psychologists deal with these very difficult issues. It’s hard to perceive the whole process,” Zimbardo said.

McFarland, whose study criticized Zimbardo’s methods, said it was important to understand the experiment, and has included the study in his psychology courses, following it with readings on massacres in Vietnam and findings of torture and severe mistreatment in Abu Ghraib prison.

“It’s a matter of balancing points and balancing perceptions, and the perception that human beings have a great capability for good and also a great capability for evil -- I think there’s certainly enough real-world experience to show that,” he said.

Melissa Smith, a fourth-year doctoral student at George Mason University studying human factors and applied cognition, had an opportunity to meet Zimbardo and the film’s director, Kyle Patrick Alvarez, before she saw the movie a few weeks later. She described the film as “gripping” and “brutal.”

She said she had first learned about the experiment in middle school but had the opportunity to see some of the actual footage of the study later. She said that juxtaposing the actual footage with the movie’s depiction might teach students about the study and the evolution of views about it.

“No one really knew the extent of the experiment because it was just another experiment,” Smith said. “I think being able to show them that and be like, ‘hey, this is real, what do you guys think?’ … I think you can show that this is a true example of people being put in a prison that still impacts daily perception of life.”

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The Stanford Prison Experiment Ethical Issues

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What was the Stanford Prison Experiment ? What were the ethical issues of the experiment?

In 1971, Philip Zimbardo turned the basement of Stanford University’s psychology building into a simulated prison, paying undergraduate male volunteers to act as prisoners and guards. Zimbardo detailed his findings in The Lucifer Effect , which discusses the nature of human evil.

Keep reading to learn more about the ethical issues of the Stanford Prison Experiment.

Ethical Issues In Stanford Prison Experiment

Decades later, psychologists still discuss the Stanford Prison Experiment’s ethical issues because of its shocking findings of human nature and the inhumane treatment of its test subjects.

While he planned to run the experiment for two weeks, Zimbardo ended it after just six days because his “prisoners” were suffering far more than he intended, largely due to their guards’ extreme abusive behavior. For example, the guards refused to let the prisoners sleep, constantly harassed them with insults and arbitrary demands, and punished them by making them exercise until they dropped.

The Stanford Prison Experiment Wasn’t Really an Experiment

Various experts have criticized the Stanford Prison Experiment for its lack of scientific rigor ever since it was publicized. The “SPE” isn’t even technically an experiment, as it has no control group or independent variable—Zimbardo admits he intended it more as a “demonstration” than an experiment. Instead of publishing his findings in a peer-reviewed journal, Zimbardo took his project directly to The New York Times for the mainstream media buzz.

This move away from traditional scientific publication channels paid off for Zimbardo: The experiment’s shocking account of abuse gripped the nation, and its notoriety earned the psychologist numerous prestigious paid positions : He made a successful documentary, authored one of the most popular psychology textbooks of the time, and hosted a 1990 documentary series titled Discovering Psychology .

1. Abusive Power Dynamics

Zimbardo states that by forcing the students into the simulated roles of “prisoner” and “guard” during the Stanford Prison Experiment and surrounding them with identity cues that reinforced this power dynamic, he created the circumstances necessary to disengage the guards’ sense of morality. After they had donned identical uniforms and spent enough time in the lifelike prison environment, the role of “guard” overwhelmed the volunteers’ normal personalities.

While they were initially merely pretending to be fearsome and domineering, within days the guards internalized this role, gaining genuine feelings of disgust toward the prisoners and escalating their cruelty far beyond what Zimbardo asked of them. The guards were the most sadistic toward the prisoners when they felt they were not being watched—they would insult and punish the prisoners more on the night shift than during the day and shove prisoners into the urinals during the presumably unobserved toilet runs. This is the opposite of what we would expect if they were just playacting for the cameras.

This situation’s identity cues transformed the prisoners’ personalities, too. After a couple of days of arbitrary punishment for senseless rules, the college-age volunteers became mindlessly obedient to the guards. Their personalities from the outside world disappeared. Rationally, they knew they were volunteers who could quit at any time, but they embraced their roles as reality so deeply that none of them really tried—they accepted their fate as helpless prisoners.

2. Social Pressures Turned to Cruelty

Zimbardo recounts how group pressure influenced the Stanford Prison Experiment guards to be crueler to the prisoners. In every shift, one guard would take the lead in abusing the prisoners, and at least one would imitate him. Quickly, tormenting the prisoners became the norm, and guards who didn’t actively do so stuck out. Many of the guards who initially didn’t want to hurt the prisoners eventually did so to fit in. No guards ever stood up to the group consensus and demanded they tone down the abuse.

The power of authoritative pressure in the Stanford Prison Experiment is best seen in the prisoners. The guards frequently used their authority to get the prisoners to degrade and harm themselves and one another, and for most of the experiment, the prisoners complied. The guards ordered the prisoners to sing songs for them, insult one another, and perform sexual pantomimes on one another. In retrospect, the guards reported being shocked by how readily the prisoners conformed to their extreme commands. They continually expected the prisoners to eventually stand up for themselves and refuse to play along, but they never did.

3. Dehumanization

Zimbardo recounts that the guards of the Stanford Prison Experiment wore identical uniforms, masked themselves with reflective sunglasses, and forced the prisoners to refer to them by title instead of their name, all of which contributed to their anonymity and self-dehumanization, disengaging their sense of morality.

There were several factors at play contributing to the prisoners’ dehumanization as well. The guards only referred to prisoners by the numbers on their jumpsuits and forbade them from using their real names. The guards also prohibited the prisoners from openly or honestly expressing their emotions, causing them to feel (and appear) less human. For these reasons, the guards reported seeing the prisoners like animals and losing their feelings of empathy for them.

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Somehow, Katie was able to pull off her childhood dream of creating a career around books after graduating with a degree in English and a concentration in Creative Writing. Her preferred genre of books has changed drastically over the years, from fantasy/dystopian young-adult to moving novels and non-fiction books on the human experience. Katie especially enjoys reading and writing about all things television, good and bad.

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Stanford Prison Experiment: The issue of Ethicality

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In 1971, a research was conducted in which subjects played the roles of prisoners and guards in a period of time simulating the prison environment for the purpose of studying a number of problems of psychological and sociological relevance. The projected two- week study had to be prematurely terminated when it became apparent that many of the ‘prisoners’ were in serious distress and many of the ‘guards’ were behaving in ways which brutalized and degraded their fellow subjects.

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Almost 50 years on, the Stanford Prison Experiment of 1971 remains one of the most notorious and controversial psychology studies ever devised. It has often been treated as a cautionary tale about what can happen in prison situations if there is inadequate staff training or safeguarding, given the inherent power differentials between staff and inmates. But what exactly was the ‘situation’ in the simulated prison at Stanford University, and how exactly did the participants respond to it? This article provides a new analysis of the behaviour of the nine Stanford ‘guards’, which draws on unpublished archival records and original interviews with some of the participants. It adopts an interactionist approach, whereby the individual backgrounds and personalities of the participants are seen to inform their behaviour within the situation provided, as well as vice versa. A key suggestion to emerge from this analysis is that the conduct of the three guard shifts, within the experiment, diffe...

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The Stanford Prison Experiment has continued to raise questions about social science research ethics. Male student volunteers were randomly assigned to be prisoners or guards in a simulation in which the guards became sadistic and the prisoners showed extreme stress. Two ethical issues are the ability of the participants to leave the experiment and the failure to provide adequate oversight and intervening to limit the abuse of the prisoners. In 2018, these issues were revisited and some declared the experiment unscientific and untrustworthy. However, the experiment was carried out before many social science research ethics were established. A detailed description of the experiment reveals insights on how group dynamics and social structure can encourage normal individuals to harm one another in a prison environment. The study is a cautionary tale that should be included in textbooks to improve social science research, demonstrate the need for research ethics, and prevent outrageous ...

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Ethical Issues With the Stanford Prison Experiment – Essay

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Nowadays, modern psychologists are expected to adhere to a strict and rigid code of ethical principles in order to ensure the validity of their practices and the safety of the patients and participants. Any psychological experiments that are to be conducted are forced to undergo an extensive review by a competent board of experts and receive their approval prior to proceeding. However, it was not always the case.

The formal acknowledgment of these ethical guidelines by the American Psychological Association happened only after the famous Stanford Prison Experiment, conducted by Professor Philip Zimbardo (“Ethical Guidelines for Human Research” par. 12). Despite the fact that the experiment provided interesting results and the data accumulated during the research was later used as a basis for improvement of prison conditions, it still violated several ethical guidelines and put the physical and mental health of the participants at unnecessary risk. The purpose of this paper is to explore the moral qualms of the Stanford Prison Experiment.

Professor Philip Zimbardo, when conducting his study, wanted to find out how readily the participants would adapt and conform to the roles of a prisoner and a guard during a roleplay exercise. The investigation was sparked by numerous reports of the brutality of the guards in prisons. This experiment was supposed to give an answer as to whether this tendency had something to do with the personalities of the guards or the environment that they found themselves in.

For this experiment, 24 participants were chosen out of 75 volunteers. The students were split in half. One group had to play the prisoners and another – the guards. The setting emphasized realism – the fake prison looked very real, and the professor even arranged an unexpected arrest of the participants in their homes by the local police department. The prisoners were told to refer to one another only by their numbers. The guards wore dark shades to avoid any direct eye contact with the prisoners. No explicit rules about prisoner conduct were given, aside from the fact that no violence was allowed. The guards were instructed to maintain order through any means necessary (Danko 1).

Although the experiment was meant to last for two weeks, it was terminated after six days. The research became famous due to the unexpected brutality that the mock guards showed towards the prisoners. All participants were tested prior to the experiment and showed no inclination towards sadistic behavior. During these six days, the guards treated the prisoners with increasing neglect, contempt, and abuse. There was one case of a prison riot when the participants barricaded themselves in their cells.

One prisoner had to be released from the experiment due to experiencing a psychological breakdown. The experiment concluded that the brutal behavior of the guards was a situational behavior and not a dispositional one (McLeod 1).

The study has received numerous criticisms concerning professional ethics. The major points of all ethical complaints include a lack of fully informed consent and endangering the participants’ mental health (“Ethical Principles of Psychologists and Code of Conduct” par. 4). The participants were unable to give fully informed consent since the professor himself was unable to predict the results of the experiment. The episode with the fake arrests was a last-minute addition that none of the participants consented to. Not only was this incident a breach of ethics, but it was also a violation of the contract Zimbardo signed with the participants (Zimbardo 1).

A much more pressing concern, however, was endangering the participants’ mental health. The students involved in the experiment were exposed to a great amount of stress, humiliation, and psychological harm. One of the prisoners suffered a mental breakdown and had to be released from his cell prematurely. He succumbed to uncontrolled bursts of screaming, crying and laughter (“The First Prisoner Released” par. 8). Although no permanent long-term effects were noticed for any of the subjects, it was still a case of dangerous misconduct. The experiment breached the general principles of psychological ethics, such as the principle Benevolence and Non-maleficence and the Respect for People’s Rights and Dignity (“Ethical Principles of Psychologists and Code of Conduct” par. 3).

Professor Zimbardo was fortunate that the experiment he conducted did not cause any lasting or permanent damage to the participants. As the incident with the breakdown of one of the students had shown, the possibilities for psychological trauma were plenty. The experiment should have been stopped after that incident. Instead, it continued for three more days and was terminated only after the interference of Christina Maslach (McLeod 1), who was brought in to conduct interviews with the guards and the prisoners.

The history of unsavory experiments shows that the experiments, which have little regard for morals and ethics, tend to lend better results. However, there is a danger in such a way of thinking. Modern psychology is dedicated to helping people and studying human behavior. These goals could be achieved without endangering those who agreed to aid the scientists in their noble goals. It should stay that way. Perhaps these measures would restrain the speed of progress. However, it is better this way. The scientific community should take care not to undermine the trust the people are putting into them. The public outrage caused by the Stanford Experiment shows how fragile that trust could be.

Works Cited

Danko, Meredith . 10 Famous Psychological Experiments That Could Never Happen Today . Web.

Ethical Guidelines for Human Research, 2016. Web.

Ethical Principles of Psychologists and Code of Conduct , 2010. Web.

McLeod, Saul. Stanford Prison Experiment . Web.

The First Prisoner Released , 2016. Web.

Zimbardo, Philip. Consent Form . Web.

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IvyPanda. (2020, October 13). Ethical Issues With the Stanford Prison Experiment – Essay.

"Ethical Issues With the Stanford Prison Experiment – Essay." IvyPanda , 13 Oct. 2020,

IvyPanda . (2020) 'Ethical Issues With the Stanford Prison Experiment – Essay'. 13 October.

IvyPanda . 2020. "Ethical Issues With the Stanford Prison Experiment – Essay." October 13, 2020.

1. IvyPanda . "Ethical Issues With the Stanford Prison Experiment – Essay." October 13, 2020.


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    Stanford Prison Experiment, a social psychology study in which college students became prisoners or guards in a simulated prison environment.The experiment, funded by the U.S. Office of Naval Research, took place at Stanford University in August 1971. It was intended to measure the effect of role-playing, labeling, and social expectations on behaviour over a period of two weeks.

  4. Stanford prison experiment

    The Stanford prison experiment (SPE) was a psychological experiment conducted in August 1971.It was a two-week simulation of a prison environment that examined the effects of situational variables on participants' reactions and behaviors. Stanford University psychology professor Philip Zimbardo led the research team who administered the study.. Participants were recruited from the local ...

  5. The dirty work of the Stanford Prison Experiment: Re-reading the

    On August 21, the day after the experiment ended, Black Panther leader George Jackson was shot dead by tower guards at California's San Quentin State Prison. The following month, a four-day hostage situation at Attica Correctional Facility, in upstate New York, was brought to an abrupt end when State Troopers retook the facility with tear gas ...

  6. Stanford Prison Experiment (SPE): Icon and Controversy

    Introduction. The Stanford Prison Experiment (SPE) took place at a time when the sources of authoritarianism and evil were a focal concern in psychology. It emerged from a tradition of activist social psychological research beginning with Solomon Asch in the 1940s and extending through Stanley Milgram's obedience experiments in the early 1960s.

  7. 50 Years On: What We've Learned From the Stanford Prison Experiment

    The Experiment in a Nutshell. In August 1971, I led a team of researchers at Stanford University to determine the psychological effects of being a guard or a prisoner. The study was funded by the ...

  8. Philip Zimbardo defends the Stanford Prison Experiment, his most ...

    Zimbardo responds to the new allegations against his work. Philip Zimbardo. Brian Resnick was Vox's science and health editor and is the co-creator of Unexplainable, Vox's podcast about ...

  9. What the Stanford Prison Experiment Taught Us

    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 ...

  10. PDF Psychological Research & Ethics: The Zimbardo Prison Experiment as a

    s PowerPoint of research/ethics information Procedures:Procedure 1: Introduce th. opic of ethics in psychological research with photos from famous experiments. Ask students what they understand by the terms "ethical" or "unethical.". Procedure 2: rison Experiment video Procedure 3: Discuss with students the que.

  11. The Stanford Prison Experiment: The Power of the Situation

    Two ethical issues raised by the SPE are the ability of subjects to withdraw from a research study at any time, and the failure to minimize harm and end the study when abusive behavior escalates. Regarding the matter of withdrawing, according to the Participant Information Sheet, "It is obviously essential that no prisoner can leave once ...

  12. What can Milgram and Zimbardo teach ethics committees and qualitative

    Philip Zimbardo's (1973) Stanford Prison Study and Stanley Milgram's (1974) Obedience study are convenient shorthand fall guys for justifying the necessity of ethics review. As with Adam and Eve's original sin producing the fall of man in the Christian faith, Zimbardo and Milgram are cast in this role, not only for use in psychology, but emblematic of the need to evaluate behavioral ...

  13. Demonstrating the Power of Social Situations via a Simulated Prison

    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).

  14. The Stanford Prison Experiment 50 Years Later: A Conversation with

    In April 1971, a seemingly innocuous ad appeared in the classifieds of the Palo Alto Times: Male college students needed for psychological study of prison life. $15 per day for 1-2 weeks.In no time, more than 70 students volunteered, and 24 were chosen. Thus began the Stanford Prison Experiment (SPE), conducted inside Jordan Hall on the Stanford campus.

  15. 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.

  16. Zimbardo prison study The Stanford prison experiment

    The Stanford Prison Experiment, led by Philip Zimbardo in 1971, explored how social norms influence behavior. Normal students, randomly assigned as prisoners or guards, adopted their roles to alarming extents. Despite knowing it was an experiment, guards enforced harsh control, while prisoners exhibited severe emotional breakdowns, leading to ...

  17. The Stanford Prison Experiment was massively influential. We just ...

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

  18. Film on Stanford prison experiment resurrects questions on ethics in

    New film renews attention on a study that is still taught in college -- and that resonates to some in light of ethics debates in psychology. The Stanford University prison experiment was abruptly ended 44 years ago after treatment of pseudoprisoners by pseudoguards, both played by students, escalated too far for the researchers to tolerate.

  19. (PDF) How to get out of the Stanford Prison Experiment: Revisiting

    The Stanford Prison Experiment has continued to raise questions about social science research ethics. ... Two ethical issues are the ability of the participants to leave the experiment and the ...

  20. PDF The Ethics of The Stanford Prison Experiment

    The Stanford Prison Experiment was a social psychology experiment conducted by Dr. Philip Zimbardo. It involved college students taking up the roles of either prisoners or guards in a simulated prison environment. It attempted to investigate the psychological effects of perceived power, focusing on the struggle between prisoners and prison ...

  21. The Stanford Prison Experiment Ethical Issues

    Ethical Issues In Stanford Prison Experiment. Decades later, psychologists still discuss the Stanford Prison Experiment's ethical issues because of its shocking findings of human nature and the inhumane treatment of its test subjects. While he planned to run the experiment for two weeks, Zimbardo ended it after just six days because his ...

  22. Stanford Prison Experiment: The issue of Ethicality

    The Stanford Prison Experiment has continued to raise questions about social science research ethics. Male student volunteers were randomly assigned to be prisoners or guards in a simulation in which the guards became sadistic and the prisoners showed extreme stress. Two ethical issues are the ability of the participants to leave the experiment ...

  23. Stanford Prison Experiment

    The major points of all ethical complaints include a lack of fully informed consent and endangering the participants' mental health ("Ethical Principles of Psychologists and Code of Conduct" par. 4). The participants were unable to give fully informed consent since the professor himself was unable to predict the results of the experiment.

  24. Inside America's least probable prison experiment

    Green Haven, an enormous, imposing building in upstate New York, is the largest maximum-security men's prison the programme has operated in, and by far the most difficult.