philip zimbardo experiment

Stanford Prison Experiment: Zimbardo’s Famous Study

Saul Mcleod, PhD

Editor-in-Chief for Simply Psychology

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

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

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Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

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

On This Page:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Asserting Authority

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

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

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

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

Physical Punishment

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

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

Asserting Independence

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

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

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

Putting Down the Rebellion

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

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

Special Privileges

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

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

Consequences of the Rebellion

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

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

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

Prisoner #8612

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

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

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

A Visit from Parents

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

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

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

Catholic Priest

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

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

Prisoner #819

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

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

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

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

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

Back to Reality

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

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

An End to the Experiment

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Critical Evaluation

Ecological validity.

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

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

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

Demand characteristics

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

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

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

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

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

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

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

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

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

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

Sample bias

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

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

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

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

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

Zimbardo’s conclusion may be wrong

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

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

Contributions to psychology

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

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

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

Contribution to prison policy

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

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

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

The authors argue psychologists should reengage to:

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

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

Evidence for situational factors

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

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

Evidence for an interactionist approach

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

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

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

Ethical Issues

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

Protection of Participants

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

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

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

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

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

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

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

Withdrawal 

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

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

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

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

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

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

Discussion Questions

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

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

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

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

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

Frequently Asked Questions

What happened to prisoner 8612 after the experiment.

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

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

Why did Zimbardo not stop the experiment?

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

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

What happened to the guards in the Stanford Prison Experiment?

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

What did Zimbardo want to find out?

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

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

What were the results of the Stanford Prison Experiment?

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

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

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

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

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

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

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

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

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

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

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

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

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

Further Information

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

Demonstrating the Power of Social Situations via a Simulated Prison Experiment

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

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

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

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

Significance

Practical application.

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

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

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

Cited Research

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

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

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

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

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

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

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

American Psychological Association, June 8, 2004

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

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

by Brian Resnick

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

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

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

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

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

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

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

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

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

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

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

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

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

Brian Resnick

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

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

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

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

So does that not invalidate the conclusion?

Philip Zimbardo

Not at all!

And why not?

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

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

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

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

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

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

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

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

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

And I reject that.

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

Zero? How can you say zero?

Okay, I can’t say.

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

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

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

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

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

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

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

Brian, I’m gonna stop you.

Can I finish the question?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

You don’t want to talk about him.

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

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

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

You don’t assume good faith on their part?

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

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

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

The view that situation can make a difference?

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

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

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

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

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

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

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

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

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

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

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

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

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

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What the Stanford Prison Experiment Taught Us

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

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

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

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

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

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• Quiet Rage: The Stanford Prison Experiment

Philip G. Zimbardo

Philip Zimbardo was born on March 23, 1933 in New York City. He attended Brooklyn College where he earned a B.A. in 1954, triple majoring in psychology, sociology and anthropology. He then went on to earn his M.A. in 1955 and his Ph.D. in 1959 from Yale University, both in psychology.

He taught briefly at Yale before becoming a psychology professor at New York University, where he taught until 1967. After a year of teaching at Columbia University, he became a faculty member at Stanford University in 1968.

Philip Zimbardo is perhaps best known for the Stanford Prison Experiment, conducted in the basement of the Stanford University psychology department in 1971. The participants in the study were 24 male college students who were randomly assigned to act either as "guards" or "prisoners" in the mock prison.

The study was initially slated to last two weeks, but had to be terminated after just six days because of the extreme reactions and behaviors of the participants. The guards began displaying cruel and sadistic behavior toward the prisoners, while the prisoners became depressed and hopeless.

Since the prison experiment, Zimbardo has continued to conduct research on a variety of topics including shyness, cult behavior and heroism. In 2002, Zimbardo was elected president of the American Psychological Association. After more than 50 years of teaching, Zimbardo retired from Stanford in 2003 but gave his last "Exploring Human Nature" lecture on March 7, 2007.

Today, he continues to work as the director of an organization he founded called the Heroic Imagination Project. The organization promotes research, education and media initiatives designed to inspire ordinary people to act as heroes and agents of social change.

• Best-Selling Books
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The Stanford Prison Experiment

Heroic imagination project (hip).

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The Lucifer Effect

Time perspective theory.

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Dr. Philip George Zimbardo – Biography

Dr. Philip George Zimbardo, a towering persona in the field of psychology, is widely recognized for his pioneering and controversial 1971 Stanford Prison Experiment . This overview will explore the life journey and illustrious career of Zimbardo, from his humble beginnings in New York City to his eventual rise to prominence as a leading American psychologist.

Zimbardo was born on March 23, 1933, in New York City, to Sicilian immigrants. His early life in a South Bronx neighborhood shaped his interest in understanding human behavior and the influence of social situations. He later attended Brooklyn College and Yale University, where he excelled academically and laid the foundation for his future contributions to psychology.

Zimbardo’s extensive research interests span across social psychology, time perspective (TP) , shyness , terrorism, and hypnosis. His pedagogical endeavors include teaching at Yale, New York University, Columbia University, and Stanford University, where he conducted the infamous Stanford Prison Experiment . This experiment , which studied the psychological effects of perceived power and the interaction between prison guards and prisoners, has had a profound impact on the field of social psychology, sparking debates on ethical standards in experimental studies.

Dr. Zimbardo’s numerous accolades and awards bear testimony to his groundbreaking work, including his presidency of the American Psychological Association. His enduring impact on contemporary psychology continues to be felt today, with his theories and research influencing both academic discourse and practical applications in the field.

Table of Contents

Dr. Philip G. Zimbardo’s infancy was characterized by the harsh realities of the Great Depression, having been born in this challenging epoch. His birthplace, the economically strained South Bronx area of New York City, was marked by widespread poverty and adversity.

The dynamics of his family unit, coupled with their financial struggles, played a significant role in molding his life path. This economic deprivation not only compelled Zimbardo to take on an assortment of jobs at an early age but potentially had a significant role in shaping his health and overall well-being during these pivotal years.

Born into a rich cultural lineage, Dr. Philip Zimbardo holds his Sicilian heritage close to his heart, a tribute to his immigrant grandfather from whom he got his name. His grandfather, Philip, hailed from Palermo, the capital of Sicily, and was a barber by profession, known for his regal persona. His grandmother, Vera, despite her petite stature, was renowned for her passionate love and care.

Dr. Zimbardo’s father, George Sr., was initially a barber like his father, carrying forward the family tradition. However, the times of World War II called for a career shift, and he adapted by becoming an electrician. Even though he faced frequent periods of unemployment, his mechanical proficiency and musical abilities added a unique flavor to the Zimbardo household.

Margaret, Dr. Zimbardo’s mother, despite not having a formal education, was the pillar of the family, steering them through life’s adversities with her innate wisdom. Their resilience was further embodied by his younger brothers George Jr. and Donald, as well as his sister Vera. Together, they painted a picture of a family standing strong in the face of trials, deeply rooted in their cultural heritage.

The impoverished upbringing of young Dr. Zimbardo, colored by both family unity and cultural vibrancy, was a stark contrast to his relentless battle with poverty. The monetary uncertainty of his family led to an unstable lifestyle characterized by regular relocations due to their inability to make consistent rent payments and a persistent, gnawing hunger.

His early intellectual growth was hindered due to the scarcity of literary resources in his home environment . Poverty had a profound impact on his physical well-being, often leading to bouts of illness during his childhood. It also influenced his perspective, compelling him to concentrate on immediate necessities over long-term aspirations.

Dr. Zimbardo’s experiences within the constraints of poverty were not solely marked by a lack of material resources. He also suffered from the degrading treatment he received at the hands of welfare workers, clinic doctors, and dentists. Even the individuals in charge of distributing welfare clothing treated him with disrespect and insensitivity.

This early exposure to the brutal aspects of poverty played a significant role in shaping Dr. Zimbardo’s later career. It fueled his quest to understand the complexities of human behavior and ignited his passion for addressing social injustices, a commitment that would remain with him for the rest of his life.

Throughout these hardships, Dr. Zimbardo was able to find solace in his relationship with his bachelor uncle, George. Despite being illiterate, Uncle George provided much-needed support in the form of food and entertainment. He would ingeniously read the Sunday comic strips, crafting inventive tales from the images, despite his inability to actually read the text. Uncle George’s creative storytelling provided a source of joy amidst the family’s struggles. His mother’s unfaltering optimism and wisdom also played a pivotal role in imparting a sense of hope for a brighter future.

Navigating the difficult socio-economic circumstances, young Zimbardo, took upon himself the responsibility of contributing to his family’s livelihood.

One of his initial endeavors was as a door-to-door magazine salesman, a role that demanded tenacity and the ability to persuade potential buyers. This experience helped shape his understanding of human psychology and decision-making behavior.

He also held a position as a laundry delivery person in the bustling neighborhood of Harlem, where he balanced hefty piles of clothing and ensured they were delivered promptly to clients, further enhancing his skills in time management and customer service.

His most notable job, however, was as a shoe shiner. His Uncle George, a shoe shiner himself, gifted him a shoeshine box that became the cornerstone of his shoe-shining venture. The location of his business, strategically positioned in front of a busy local bank on Southern Boulevard, ensured a steady stream of customers and the business thrived.

Unfortunately, this venture was short-lived as his Uncle Norman, feeling embarrassed by the public nature of the job, coerced him into quitting. Despite the setbacks, these diverse job experiences during his formative years played a crucial role in shaping Dr. Zimbardo’s professional trajectory. They exposed him to a myriad of skill sets and taught him invaluable life lessons that influenced his future career path.

From his early years, Dr. Zimbardo’s life was characterized by a profound tenacity and resolve to conquer physical hardship. His health was continually undermined by the repercussions of an inadequate diet, exposure to second-hand smoke, and recurrent illnesses due to a compromised immune system. His formative years were punctuated by recurrent episodes of pneumonia, asthma flare-ups, and prolonged periods in hospital care.

A defining phase in his life took place when he was merely five and a half years old, marked by a six-month stay at the Willard Parker Hospital, recognized for treating contagious diseases. This demanding ordeal played a significant role in shaping his emerging character, ethical beliefs, and subsequent professional decisions.

Zimbardo found his inspiration in the life of Theodore Roosevelt, the 26th President of the United States, who was known for his vigor and resilience. This motivated Zimbardo to set out on a transformative journey towards better health and fitness. During his adolescent years, from 12 to 15, he regularly engaged in hiking and camping activities, which contributed to his health improvement and physical strength. By shouldering heavy backpacks and involving himself in various outdoor sports like softball, baseball, and track events, he gradually built up his strength, enabling him to overcome his health adversities.

Dr. Zimbardo’s initial schooling was in New York City, where he attended two public schools – P.S. 25 for his elementary education and P.S. 52 for his junior high studies. His educational voyage was marked by a series of transitions through different high schools. This experience highlighted the trials he encountered during his developmental years. Despite these hurdles, Dr. Zimbardo held fast to his academic aspirations, demonstrating resilience and tenacity in his pursuit of higher education.

His unwavering commitment led him to the portals of an esteemed college and subsequently a prestigious graduate school. It was here, immersed in academia, that he polished his scholarly abilities and discovered a burning interest in the study of psychology. This field would later see him as a key contributor.

High School

In his high school days, Philip Zimbardo, attended a variety of educational institutions. He began his high school journey at JHS located in New York during his freshman year. His sophomore year was a combination of experiences at Stuyvesant High School in New York, a prestigious school known for its academic rigor, and James Monroe High School in the northern region of Bronx, an ethnically diverse area.

In 1947, Zimbardo relocated to California, where he attended North Hollywood High School for his junior year. Unfortunately, he faced severe social exclusion here, which led to the development of psychosomatic asthma, a condition where psychological distress manifests as physical symptoms.

However, Zimbardo overcame these challenges and returned to James Monroe H.S. for his senior year. It is here that he displayed his leadership potential, a perfect combination of academic prowess and street intelligence. His peers recognized his skills and elected him as the team captain and class president. Furthermore, he was voted as the most popular boy and was awarded the nickname ‘Jimmie Monroe’. Zimbardo’s academic excellence also led him to be named Valedictorian of his graduating class.

An important friendship Zimbardo fostered during high school was with Stanley Milgram, who would later earn recognition as a significant psychological researcher. Intriguingly, Zimbardo found himself interacting more with female students and minority students over his white male peers, finding these groups less rivalrous and more attuned to interpersonal dynamics.

This transformative high school journey equipped Dr. Zimbardo with the foundational skills, resilience, and experience that propelled him to excel in his college years and beyond in his illustrious career in psychology.

Dr. Zimbardo encountered significant pressure during his college years. Particularly from his father who had envisioned him embarking on a full-time job immediately after high school. Nevertheless, he struck a balance by enrolling in Brooklyn College, a four-year institution that offered tuition-free education.

Dr. Zimbardo, displayed exceptional determination in navigating the challenging landscape of higher education, a journey deeply influenced by his father’s staunch belief in self-reliance. Coming from an Italian immigrant family, Zimbardo worked hard to balance his job, scholarly pursuits, and preparations for his future in graduate school.

His daily journey entailed a taxing three-hour commute to Brooklyn College. Despite the extensive travel time to and from college and his participation in numerous extracurricular activities, he devoted his evenings and the entirety of his Saturdays to work. In doing so, he was able to maintain financial self-sufficiency and reduce his reliance on his father’s financial support.

Zimbardo’s college life was not merely limited to academia. He was also active in sports and assumed leadership roles in his fraternity, Pi Beta Gamma. This involvement hints at a balanced and comprehensive approach to college life that would lay the foundation for his future achievements.

Expectations

As a young, eager student at Brooklyn College in the late 1950s, Zimbardo was thrilled about enrolling in an introductory course to psychology for his first year. However, contrary to his initial enthusiasm, he discovered the course to be a letdown, characterizing it as the most unsatisfactory course he had ever undertaken. After the disappointing psychology course, Dr. Zimbardo switched his major to Sociology.

The influence of several of his professors was instrumental in shaping Dr. Zimbardo’s academic pursuits.

• Dr. Zimbardo was introduced to the NAACP by Professor Charles Radford Lawrence.
• Professor Felix Gross influenced Dr. Zimbardo’s understanding of European social movements and revolutions.
• Dr. Zimbardo contributed to Professor Felix Gross’s book, resulting in his first citation in print.

Zimbardo also undertook three pioneering research projects that were significantly advanced for their time. In his senior year, he reintroduced psychology into his academic portfolio, choosing it as a second major. He simultaneously held the position of a paid research assistant, gaining practical experience in the field.

His practical research experience further enriched his knowledge, ultimately allowing him to excel in his chosen fields of Sociology and Psychology.

Dr. Zimbardo earned his B.A. degree from Brooklyn College in 1954, where he majored in three distinct fields: psychology, sociology, and anthropology.

While attending Brooklyn college, Dr. Zimbrado took up a position at the St. James Theater in New York. This experience came his way through a recommendation from his close friend, Gene Wolkoff, and offered him a modest remuneration of $3.00 per show.

His job responsibilities included selling a range of items including candy and drinks, as well as programs, and also involved in the checking of hats and coats. This role offered him an extraordinary opportunity to witness a multitude of Broadway performances and participate in after-show parties with the cast members. It also led him to establish connections with many illustrious figures in the entertainment industry such as Richard Rogers, Oscar Hammerstein, Ray Bolger, Mary Martin, Gertrude Lawrence, and Yul Brynner.

This show biz job also exposed him to the underhanded business practices prevalent in the industry, and these experiences significantly influenced his later doctoral work as a social psychologist.

Preparing for Grad School

Fueled by an inherent love for knowledge, Dr. Zimbardo, chose to extend his academic journey beyond his undergraduate studies, with a firm focus on pursuing a graduate degree.

His inspiration for this decision was Raef Haddad, a noteworthy personality in his life, who had a significant influence on his parents, thus leading them to support Dr. Zimbardo’s academic aspirations.

His academic prowess facilitated a full-tuition assistantship along with a stipend at the prestigious Yale University, an Ivy League institution known for its rigorous academic programs. Zimbardo successfully completed his Master’s degree in an impressive span of one year (1955). This achievement was not without its challenges, as he encountered issues related to racial identity during the application process, a reflection of the societal hurdles of his time.

Graduate School

During his tenure at Yale University for graduate studies between 1954 and 1960, Dr. Philip Zimbardo underwent a transformational journey that greatly influenced his career in the discipline of psychology.

Initially, he found himself grappling with the intense academic competition, feeling somewhat inadequate in his first term and even contemplated withdrawing. However, heeding his mother’s wise counsel, he persevered for another term, and gradually adjusted to the rigorous academic culture at Yale and received his Ph.D in 1959.

His collaboration with scholars like Neal Miller and Carl Hovland had considerable impact on his research direction. Simultaneously, Dr. Zimbardo took his first steps towards his teaching career, co-directing a project focused on test anxiety . This research was met with international interest, leading him to present his findings on a global stage.

Dr. Zimbardo also engaged in research focused on the exploratory behavior of male albino rats, a project he worked on under the supervision of Prof. K.C. Montgomery. Tragically, Montgomery later succumbed to depression and took his own life, leaving a void in Dr. Zimbardo’s academic journey. Nevertheless, Dr. Zimbardo continued his research pursuits, publishing several studies under the mentorship of Fred Sheffield.

His fascination with psychology also led him to explore the study of animal sexual behavior, under the guidance of Frank Beach. Together, they co-authored an enlightening study on the impact of chlorpromazine and caffeine on the sexual behavior of male rats.

Dr. Zimbardo also collaborated with Hovland on a project investigating judgment in ambiguous situations. His dissertation research was an interesting comparison of predictions from contrast-assimilation theory and dissonance theory.

In addition to his research endeavors, Dr. Zimbardo taught an introductory psychology class, fostering the next generation of psychologists. He also presented a study at an International Congress of Psychology, a prestigious global platform for experts in the field.

Dr. Zimbardo’s time at Yale was marked by an exposure to a trove of knowledge and the opportunity to learn from eminent psychologists. It was a time that undoubtedly shaped his future career and contributions to the field of psychology.

Throughout his illustrious career as an educator, Dr. Philip Zimbardo has left a significant mark on the world of academia.

Starting in 1960, he began his teaching journey at New York University, a private research institution founded in 1831. His innovative pedagogical methods made a significant impact, and in 1967, he moved to Columbia University, an Ivy League institution known for its rigorous academic standards. This move further underscored his reputation as a leading educator.

In 1968, Dr. Zimbardo took his unique teaching approaches to Stanford University, an institution famous for its entrepreneurial character located in California’s Silicon Valley. Here, he continued to shape minds, contributing to the university’s reputation for world-class education.

Dr. Zimbardo also taught at the Naval Postgraduate School in Monterey, CA. He taught a course titled “Exploring Human Nature” at the Pacific Graduate School of Psychology (PGSP).

Each of these esteemed institutions has been both influenced by and influential to Dr. Zimbardo’s teaching methods, making his career in academia a significant aspect of his professional life. His lasting influence across these decades and prestigious institutions is a testament to his dedication to education and innovative teaching practices.

NYU (1960-67)

While serving as a professor at New York University from 1960 to 1967, Dr. Zimbardo developed a profound passion for imparting knowledge in the field of psychology, even in the midst of a demanding teaching schedule. His course offerings spanned a wide array of topics, including but not limited to comprehensive introductory courses and more specialized social psychology classes.

It was during this time at NYU that he initiated his groundbreaking research in several areas of psychology. These included the study of affiliation and the psychological mechanisms that underpin it, cognitive dissonance and its impact on human behavior and decision-making, the concept and implications of conjugate reinforcement , the art and science of persuasion and attitude change, and the phenomenon of deindividuation and its correlation with anti-social behavior.

Despite some personal and professional obstacles he encountered, Zimbardo’s unwavering commitment to the advancement of academia and the bolstering of psychological research remained resilient.

His tenure at NYU played a significant role in shaping his career and contributing to the field of psychology.

In the crucial historical era from 1960 to 1967, Philip Zimbardo, was deeply motivated towards activism. This commitment was triggered by two key geopolitical events of the time: the Cuban Missile Crisis of 1962, a 13-day confrontation between the United States and the Soviet Union over the deployment of nuclear-armed missiles in Cuba; and the escalating Vietnam War, a long, costly armed conflict that pitted the communist regime of North Vietnam against South Vietnam and its principal ally, the United States.

Zimbardo’s activism took various forms, including the organization of academic forums known as teach-ins and the staging of protests. He also leveraged his academic skills for public good by creating effective initiatives for the Harlem Summer Project, a program aimed at addressing the socio-economic disparities in the Harlem neighborhood of New York City. This exemplified how his academic prowess was coupled with a profound sense of social responsibility.

In 1965, he spearheaded one of the earliest all-night teach-ins in the country. These teach-ins originated as a form of protest during the Vietnam War, where people would gather to engage in lectures and discussions about the war and related issues. Through this, Zimbardo emphasized the role of education in addressing critical social and political issues, thus raising public awareness.

Dr. Zimbardo also led a walk-out at an NYU graduation ceremony in protest of the decision to award an honorary degree to Robert McNamara, the then US Secretary of Defense, who was a controversial figure due to his role in escalating the Vietnam War.

His activism was not confined to the academic sphere. Dr. Zimbardo was also involved in protest movements in major U.S. cities, including New York City, the birthplace of many social and political movements, and Washington, D.C., the nation’s capital and a hub for political activism.

His commitment to activism did not wane when he moved to Stanford University. Instead, he continued his advocacy work throughout his illustrious career. His legacy in activism serves as a testament to his dedication to social change and justice.

Life-changing Experiences

Philip Zimbardo’s teaching stint at the prestigious New York University (NYU), which spanned from 1960 to 1967, served as a pivotal period in his professional journey, rich with transformative experiences that shaped his life.

Adding to his rich academic journey, he attended research symposiums steered by the esteemed social psychologist Leon Festinger, a pioneer in the field and the originator of social comparison theory as well as cognitive dissonance theory.

Zimbardo’s pedagogical journey wasn’t confined to the United States; his academic pursuits carried him overseas to Leuven, Belgium in 1966. There, he instructed at a summer school, exposing him to a diverse spectrum of advanced European graduate students and fellow social psychologists.

In addition to his work at NYU, Dr. Zimbardo also had the opportunity to disseminate his knowledge globally, delivering lectures at the prestigious Sorbonne in Paris, a hub of intellectual and scholarly pursuit. This international exposure broadened his horizons and his understanding of psychology’s global context.

Nationwide Recognition

Driven by a desire to increase his income and establish a stronger academic reputation, Zimbardo pursued an early promotion. However, he encountered opposition from more senior faculty members, perhaps reflecting the academic culture at the time. Undeterred, Zimbardo launched a strategic campaign to raise his national profile.

Heeding their advice, Dr. Zimbardo redoubled his endeavors to increase his publication output and was often asked to deliver lectures at scholarly gatherings around the country. As a result, he gained significant nationwide recognition which undeniably broadened his impact within the academic sphere.

This increased visibility was instrumental in advancing his career and enabled him to surmount the initial challenges he faced at NYU. His efforts also underscored the importance of national recognition in academia.

Columbia University (1967-68)

In the academic period spanning from 1967 to 1968, Dr. Philip Zimbardo held a bi-weekly teaching position at Barnard College, a liberal arts women’s college affiliated with Columbia University. Simultaneously, he was a key contributor to the Columbia Social Psychology program. In this period, Zimbardo stepped into the shoes of Bill McGuire for a year, a move that underscored his burgeoning reputation in the sphere of social psychology.

Zimbardo’s stint at Columbia was marked by a high degree of productivity and collaboration. He worked in close association with two promising graduate students, Lee Ross and Judy Rodin, playing a pivotal role in shaping their academic trajectories and paving the way for their future careers. His mentorship was instrumental in Ross landing a coveted position at Stanford University, a leading research institution in California. Similarly, Rodin went on to succeed Zimbardo at New York University, another prestigious institution known for its strong program in social psychology.

These instances from Zimbardo’s tenure at Columbia University serve as a testament to his dedication to teaching and his knack for grooming the next generation of psychologists. They also highlight his substantial impact in the realm of social psychology, a discipline that explores how people’s thoughts, feelings, and behaviors are influenced by the actual, imagined, or implied presence of others.

Stanford University (1968-current)

At the prestigious Stanford University, where he has been a faculty member since 1968, Dr. Philip Zimbardo has been a cornerstone of the Stanford University psychology department and academic community, dedicating his career to educating students in both classroom settings and seminar formats.

Throughout his tenure, he has imparted knowledge in a myriad of subjects, one of the most notable being the well-attended Introductory Psychology course, which consistently attracted hundreds of eager students.

Dr. Zimbardo is credited with the development of an innovative seminar, Practicum in Teaching. This program was designed to equip both graduate and undergraduate teaching assistants with the necessary skills and mentorship to excel in their future teaching careers.

Dr. Zimbardo also gained significant recognition for spearheading the Stanford Prison Experiment (SPE) in 1971. This psychological study sought to explore the mental implications of perceived power dynamics, with an emphasis on the tension between professional obligations and leisure activities.

The experiment has left a profound impact on the field of psychology, although it has encountered a variety of criticisms and opposing viewpoints throughout the years.

Stanford Prison Experiment (SPE)

In 1971, Stanford University was the site of a seminal social psychology experiment presided over by Dr. Philip G. Zimbardo, known as the Stanford Prison Experiment (SPE). This study, financially supported by the U.S. Office of Naval Research, involved undergraduate students from Stanford imitating the roles of both prisoners and guards in a mock prison setup.

The experiment was initially intended to last for two weeks, but it was prematurely terminated after just six days due to the unexpectedly severe and disturbing behavior that emerged.

The participants, male college students, particularly those playing the role of guards, rapidly assimilated into their roles to a troubling extent, showcasing a stark demonstration of the influence of situational factors and power dynamics on human behavior.

Zimbardo’s controversial findings from the SPE remain a matter of academic and ethical debate, offering a profound insight into the darker aspects of human nature when placed in positions of absolute power and subjugation.

Dr. Zimbardo was intrigued by the impact of situational forces and social roles on individual behavior and personal identities. His interest was primarily rooted in the concept of deindividuation, a psychological state where individuals lose self-awareness in groups, leading to anonymity and often, antisocial behavior.

His curiosity was further piqued by the Milgram Experiment’s findings, which indicated a high level of obedience towards authority figures, even in ethically questionable situations. These foundational theories and ideas provided the underpinning for Zimbardo’s seminal experiment, aimed at investigating the psychological effects of perceived power, focusing on the struggle between prisoners and prison officers in a simulated environment.

Although the Stanford Prison Experiment was fundamentally a role-playing exercise, it was meticulously designed to replicate, as closely as possible, the conditions and atmosphere of a real prison, in order to scrutinize the psychological effects of power dynamics between prisoners and prison guards.

Participants were randomly assigned roles and subjected to a simulated environment, including a mock arrest by actual police and confinement in a makeshift prison in Stanford’s psychology building.

Guards, equipped with uniforms, mirrored sunglasses, and wooden batons, were instructed to foster a sense of submissiveness and helplessness among prisoners, while avoiding physical abuse.

The experiment was closely monitored and recorded, with Zimbardo himself taking on the role of Superintendent, further blurring the lines between simulation and actuality.

The experiment’s outcome, marked by escalating cruelty and psychological trauma, sparked worldwide attention and intense debates about the ethics of such research. As the guards imposed a tyrannical regime, the prisoners responded with rebellion, depression, and disorientation. Three prisoners were so traumatized they had to be released within four days.

The sixth day saw termination of the experiment, prompted by external shock at the conditions. Furthermore, revelations of the guards’ admitted role-playing raised questions about the experiment’s authenticity.

The results, which underwent peer review, were published in several notable journals and books. Zimbardo himself drew parallels between the experiment’s findings and real-world prison atrocities, suggesting the profound implications of the observed behaviors in controlled settings.

Criticisms and Counterarguments

Despite the profound implications drawn from the experiment, numerous criticisms and counterarguments have since emerged, challenging the validity and ethical conduct of Zimbardo’s study.

Critics argue that the study lacked ecological validity due to its artificial environment, and thus, conclusions drawn may not be universally applicable. The selection bias in choosing emotionally stable individuals also undermines the study’s generalizability.

Ethical concerns revolve around the extreme psychological distress inflicted on participants, deemed unacceptable in modern research guidelines. Zimbardo’s dual role as prison superintendent and primary researcher is also criticized, suggesting possible bias in data interpretation.

Furthermore, the presence of demand characteristics, where participants acted in perceived expected ways, challenges the authenticity of observed behaviors.

In response to these criticisms, Dr. Zimbardo defended his experiment by citing the profound influence of social forces and the impact of environmental contingencies on human behavior. His defense was rooted in his belief that these factors play a significant role in shaping human actions and reactions.

Dr. Zimbardo further argued that the pressure exerted on the guards, who were participants in the study, was actually less intense than what is experienced in real-world prison settings. This argument aimed to highlight the authenticity of the participants’ actions during the study.

Despite these criticisms and Dr. Zimbardo’s subsequent defenses, the Stanford Prison Experiment continues to hold a significant place in psychological research. It has not only influenced a plethora of films and studies but has also contributed to our understanding of human behavior under imposed roles and authority settings.

Honors & Awards

Throughout his distinguished career as a psychologist, Dr. Philip Zimbardo has repeatedly been acknowledged with esteemed awards and honors, reflecting his significant impact in the realm of psychological science. Among these illustrious recognitions, the Vaclav Havel Foundation Prize stands out, showcasing his lifetime of intense research into human psychology. This global honor underlines his exhaustive work in deciphering the intricate patterns of human behavior.

Dr. Zimbardo’s roles in leading positions within key organizations emphasize his dedication to the field of psychology. His tenure as the former president of the American Psychological Association— a pivotal professional body— allowed him to shape the future and policies of the association. Similarly, his period of service as the past president of the Western Psychological Association highlights his consistent engagement with the scholarly community. He also served as the Chair of the Council of Scientific Society Presidents (CSSP), representing 63 scientific, math, and technical associations with 1.5 million members

Dr. Zimbardo’s sphere of influence, which spans education, research, writing, and professional service, has been acknowledged through a variety of accolades. These honors not only highlight his personal achievements but also his unwavering commitment to pushing the boundaries of psychological science.

Moreover, Dr. Zimbardo’s position as the Chair of the Council of Scientific Society Presidents, representing a vast network of associations across the scientific, mathematical, and technical sectors, showcased his interdisciplinary reach. His stewardship of the Western Psychological Foundation further emphasized his commitment to fostering the development of psychology.

Research Interests

Dr. Philip Zimbardo, has a broad spectrum of research interests. His research topics have included prejudice , affiliation, dissonance, persuasion, motivation , deindividuation, aggression , vandalism, cults, mind control, memory , shyness, pro-social and anti-social behavior, time perspective , madness, evil, prisons, political psychology, torture, ethics, heroism, and the teaching of psychology.

He is perhaps best known for his work on the Stanford Prison Experiment, which explored the psychological transformation of individuals when they are given complete control over others. This experiment formed the basis for his extensive research into the psychological factors that lead individuals towards evil actions.

Beyond this, he has also been involved in the study of madness, examining the different ways in which it manifests in individuals and how it affects societal perceptions.

His research on ‘time perspective’ is another significant contribution to the field of psychology. He has extensively studied how different individuals perceive time and its implications on their decision-making process and overall life trajectory.

Dr. Zimbardo led groundbreaking research on the phenomenon of shyness, particularly its impact on interpersonal relationships and self-esteem . His work on this subject has been instrumental in understanding the psychological causes and effects of shyness, and in developing strategies to manage it.

He has studied the dynamics of heroic action, to understand what motivates individuals to act heroically in certain situations. His research in this area has helped to shed light on the psychological aspects of heroism and altruism .

Dr. Zimbardo has also studied interrogation procedures used by the military and by Greek and Brazilian police torturers.

Zimbardo’s contributions extend beyond the academic world. He served as an expert witness in the infamous Abu Ghraib Prison abuses case, providing his professional opinion based on his extensive knowledge and research. His studies on the military’s interrogation procedures have offered a deeper understanding of the psychological tactics used in such situations.

According to Zimbardo,  “If you want to change a person, you’ve got to change the situation.”

Through his thorough and meticulous examinations of these topics, Dr. Zimbardo has significantly enriched our understanding of human behavior. His research contributions have been instrumental in unraveling the complexities of the human mind and the myriad factors that shape our actions and behaviors.

Dr. Philip Zimbardo has dedicated a large portion of his professional life to studying Time Perspective Theory, a concept that delves deep into the mental processes individuals use to assign their experiences to specific time categories. His research encompasses the analysis of how people perceive and classify their past, present, and future experiences, as well as those beyond the human lifespan, known as the Transcendental Future.

Zimbardo’s work also casts light on the phenomenon of temporal biases, which refers to the irregularities in the cognitive assignment of experiences to time categories based on differing circumstances and requirements. As an instrument to measure these variances in individual perceptions of time, Zimbardo, along with his research team, created the Zimbardo Time Perspective Inventory (ZTPI). This tool has proven instrumental in understanding the nuances of subjective time perspectives, thereby setting a new standard in the niche field of temporal psychology.

Philip Zimbardo made a significant contribution to the field of psychology with his extensive research on the Time Perspective Theory.

Alongside his colleague John Boyd, Zimbardo not only proposed this theory but also established it as a fundamental process in the field of psychology. They have developed a reliable index for measuring time perspective profiles, further expanding the theory’s scope. Their collective insights and findings are detailed in their collaborative book, The Time Paradox (2008). Simon and Schuster.

This groundbreaking theory investigates the unique ways in which individuals compartmentalize their experiences into temporal categories: the past, present, and future. Drawing on his rich academic background and his penchant for using a combination of various research methods, Zimbardo’s work underscores how these divisions of time shape and influence human cognition , behavior, and decision-making processes.

His significant findings, underpinning Time Perspective Theory, have broad implications across a variety of fields, not limited to psychology alone. They contribute valuable insights into educational strategies, family relationship dynamics, and social issues, emphasizing the importance of understanding and managing one’s time perspective.

This comprehension of how we perceive time can lead to better decision making, improved mental health, and a more balanced lifestyle.

Dr. Zimbardo along with clinicians Richard & Rosemary Sword also authored the book “The Time Cure” (2012). Jossey-Bass. The Time Cure presents a comprehensive guide to Time Perspective Therapy, a method demonstrated to be successful for various individuals including veterans, and those who have experienced abuse, accidents, assault, or neglect. Based on sound psychological research, the book is enriched with powerful and motivational anecdotes from individuals who have lived with PTSD, making it a valuable resource for those pursuing self-improvement, their family and friends, as well as therapists, counselors, and anyone aspiring to a more hopeful and positive future.

Dr. Philip Zimbardo’s research influences also extend into the realm of mental health disorders, specifically focusing on how normal individuals develop psychopathology, a study of mental illnesses. His theory, named the Discontinuity Theory, investigates how substantial personal disturbances can trigger symptoms associated with madness.

To study this, Zimbardo applies a model of experimental psychopathology, a field that researches the causes and processes of mental disorders through controlled experiments. His innovative approach involves creating these disruptions using post-hypnotic suggestions, a technique where hypnotized individuals are given instructions to be carried out when they’re awake.

Zimbardo’s goal is to shed light on the cognitive, emotional, and social processes that happen during this, and how these processes might be misunderstood or misattributed. His work has significantly contributed to the understanding of how personal disruptions can lead to mental health issues, bridging the gap between normality and mental disorder.

The Discontinuity Theory of the Origins of Madness

The Discontinuity Theory of the Origins of Madness, a significant sphere of investigation for Phillip Zimbardo, strives to decipher the mechanisms by which generally stable individuals can spiral into pathological cognitive, emotional, and behavioral patterns. This transition is initiated by the individual’s awareness of personal discontinuity, a sensation of a break in one’s normal continuity of experiences and self-perception.

As per the theory, cognitive biases, which are systematic errors in thinking that influence the decisions and judgments that people make, can subsequently manipulate the individual’s pursuit of understanding this discontinuity, culminating in irrational, symptomatic interpretations. These cognitive biases, deeply rooted in human cognition, can include biases like confirmation bias, where individuals favor information that confirms their preexisting beliefs, or the availability heuristic , where individuals rely on immediate examples that come to mind when evaluating a specific topic, concept, method or decision.

Each of these skewed biases can pave the way to distinct forms of mental illness, for instance, phobias, which are type of anxiety disorder defined by a persistent and excessive fear of an object or situation, or paranoia, a thought process believed to be heavily influenced by anxiety or fear, often to the point of irrationality and delusion.

This theory thus offers a comprehensive framework to understand the genesis and progression of mental illnesses.

Known for his extensive research on human behavior, Dr. Philip Zimbardo has profoundly explored the concept of evil, a topic that has fascinated him throughout his academic career. His most recognized work, the Stanford Prison Experiment conducted in 1971, was a psychological study of the human response to captivity, in which the subjects, all Stanford University students, were randomly assigned roles of prisoners or guards. The six-day experiment was intended to observe the psychological effects of perceived power and the interaction between prisoners and prison officers. This experiment and its alarming results led Dr. Zimbardo to develop ‘ The Lucifer Effect ‘, a study that investigates how ordinary people can transform into the perpetrators of evil under certain circumstances.

Dr. Zimbardo’s exploration continues to seek a deeper understanding of the factors that drive average individuals to commit heinous acts under specific social and situational variables. His work is a further investigation into the ‘banality of evil’, a term coined by political theorist Hannah Arendt, which is used to describe the capacity of ordinary people to commit atrocities under the influence of authoritative figures or oppressive systems.

Dr. Zimbardo also investigated the nature of training young men to become torturers for the State in Brazil during the military junta, collaborating with Martha Huggins and Mika Haritos-Fatouros. The results of this research are documented in “Violence Workers” published by U.C. Berkeley Press in 2002.

Dr. Zimbardo’s studies have provided significant insights into the dark side of human nature and the situational and systemic forces that can influence individuals to act against their moral compass. These insights have greatly contributed to the field of social psychology and our understanding of human behavior in extreme circumstances.

Dr. Philip Zimbardo, has dedicated a significant portion of his academic career to studying the psychological underpinnings of evil. These interests are thoroughly examined in his New York Times best-selling book, ‘The Lucifer Effect : Understanding How Good People Turn Evil.’ (2007). Random House Publishing Group.

In this seminal work, Zimbardo applies his extensive knowledge of social psychology to delve into the complex psychosocial processes that can lead ordinary people to commit extraordinarily heinous acts.

These insights are particularly applied to the shocking incidents of torture and abuse that occurred at Iraq’s notorious Abu Ghraib Prison in 2003. Drawing from his research, Zimbardo proposes a novel approach to understanding evil, focusing on situational influences and societal pressures rather than traditional trait-based theories.

‘The Lucifer Effect’ was recognized by the American Psychological Association with the prestigious William James Book Award in 2008. It features extensive research on a range of psychological phenomena, such as conformity , moral disengagement, and the bystander effect – all of which contribute to our understanding of how ordinary people can engage in extraordinary acts of evil.

The book offers valuable guidance on how to stand up against negative influences, empowering readers with tools to maintain their integrity in adverse circumstances. This groundbreaking work is a testament to Zimbardo’s commitment to unraveling the complexities of human nature and moral choices.

His theories suggest that external circumstances can be powerful enough to seduce or manipulate otherwise average individuals into becoming perpetrators of evil.

Dr. Philip Zimbardo, has made significant strides in the field of shyness research. His studies have influenced both social and personality psychology, as well as clinical psychology, deepening our understanding of introverted behaviors.

Zimbardo established the Shyness Clinic , which is now part of Pacific Graduate School of Psychology’s (PGSP) Gronowski Center, named after Andrew Gronowski, a strong advocate for community mental health. The center provides therapeutic services to those grappling with severe shyness. This practical work has allowed Zimbardo to advance his theoretical knowledge on the subject.

Currently, his research is focused on an interesting hypothesis that heavy use of electronic technology could be contributing to increased levels of shyness. He suggests that the rise in technology usage, particularly among younger generations, is creating an ‘A-Social’ environment. This term refers to an atmosphere where face-to-face social interactions are replaced by virtual ones, possibly leading to an increase in shy behaviors.

Shyness Clinic & Research

Philip Zimbardo founded The Shyness Clinic at Stanford University in the late 1970s. This innovative endeavor was one of the first of its kind, aiming to delve into the mental processes of shy individuals and create customized therapeutic interventions.

Applying the principles of his research in social psychology, Zimbardo’s clinic uses a unique ‘social fitness model’. This model emphasizes the importance of challenging dysfunctional thought patterns, cultivating new behavioral strategies, and promoting social engagement as if it were a form of exercise.

The fundamental goal of the Shyness Clinic extends beyond merely treating symptoms. It aims to alleviate the emotional distress associated with shyness and to prevent it from becoming a barrier in career advancement or the development of personal relationships. By doing so, the clinic embodies Zimbardo’s broader vision of psychology as a discipline that can transform lives by enabling individuals to overcome personal obstacles.

The services of the Shyness Clinic are accessible in various formats, in-person (Palo Alto), over the telephone, and via email, making the clinic readily available to individuals throughout the expansive San Francisco Bay Area. This wide range of service delivery options aligns with Stanford University’s commitment to community outreach and accessibility.

Heroic Action

Dr. Philip Zimbardo, has extended his research into the realm of ‘heroic action’. This area of study forms an integral part of his extensive research portfolio. His fascination with understanding what drives people to defy authority or engage in whistleblowing activities forms the backbone of his research.

A crucial aspect of his work in this field is the Heroic Imagination Project (HIP) , a theoretical framework he devised to explore deeper into the understanding of how ordinary people can manifest extraordinary acts of heroism in their everyday lives. With HIP, Zimbardo seeks to shed light on the intricate psychological mechanisms that enable individuals to defy dominant authority figures, a phenomenon often linked to his earlier work on authority and power.

He also examines the personal sacrifices and potential repercussions that individuals may face in their pursuit of such heroic deeds. This exploration is a further extension of his lifelong commitment to understanding human behavior under challenging circumstances.

The concept of ‘banality of evil,’ a term coined by political theorist Hannah Arendt, is central to Zimbardo’s research. He examines how seemingly ordinary people can be led to perform evil acts under certain conditions, but also how ordinary people have the potential to perform extraordinarily heroic acts under the right circumstances. By doing so, Zimbardo’s work highlights the convoluted facets of heroism and underscores the value of preparing individuals to act selflessly for the welfare of others.

This research thus provides a comprehensive understanding of the complexities behind our actions and the potential we all harbor for heroic deeds.

As a pioneer in the field of psychology, HIP is another testament to Zimbardo’s commitment to societal improvement. With the aim to make heroism a universal concept, HIP employs a combination of educational programs and online materials.

The project’s ultimate goal is to cultivate Heroes-in-Waiting, individuals who are primed to respond heroically when the situation demands. This initiative serves as a powerful counterforce to societal wrongdoings, further reinforcing Zimbardo’s long-standing dedication to battling negative social influences.

Zimbardo’s focus is not just on adults, but also on instilling this ‘heroic imagination’ in younger generations, such as children. He believes that empowering children to step up in challenging situations can help shape a more compassionate and courageous society.

Believing that the antidote to societal evil lies in the promotion of heroism, Dr. Zimbardo has a vision of nurturing this concept in the global consciousness . To this end, he has embarked on an innovative educational initiative to create a curriculum that fosters the heroic imagination.

This curriculum utilizes various mediums such as web-based materials, interactive games, engaging videos, and thought-provoking movies to disseminate the ethos of heroism far and wide. Dr. Zimbardo’s influential lecture at the prestigious TED conference, a global platform for spreading ideas, has garnered wide recognition, both nationally and internationally.

His work has been instrumental in sparking a dialogue about the potential for heroism that lies within each of us. To learn more about this fascinating subject, visit HeroicImagination.org , a repository of information about the Heroic Imagination Project and its mission.

Dr. Philip Zimbardo is renowned for his extensive research into the psychological impacts of military life. His main focus lies on the exploration of Social Intensity Syndrome (SIS). This psychological occurrence is commonly observed in high-intensity group settings, with the military being a prime example.

In the armed forces, units often operate in extreme conditions and are heavily reliant on teamwork and camaraderie. This intense socialization can lead to SIS, which can significantly alter a soldier’s mental state and behavior, especially in combat situations.

Dr. Zimbardo’s work involves an in-depth analysis of this syndrome. Through rigorous research and studies, he aims to uncover the profound effects that SIS can have on military personnel. His examination of SIS within the specific context of military life not only provides valuable insights into the psychological transformations of soldiers but also contributes to a broader understanding of the human psyche under severe stress and pressure.

Social Intensity Syndrome (SIS)

Dr. Zimbardo’s studies on the military have primarily focused on the Social Intensity Syndrome (SIS), a condition characterized by the intense socialization that soldiers experience in combat zones. His work has illuminated the profound and long-lasting effects of this syndrome on the mindset and mental health of military personnel.

This syndrome, often triggered by the extreme conditions and close-knit relationships formed in combat, can significantly impact a soldier’s post-combat life.

This led to the development and validation of SIS through stringent experimentation and scrutiny, establishing it as a trusted framework for investigating the process of military socialization.

SIS, which is characterized by the strong masculine social bonds in groups like the military, is measured through a comprehensive model and an accompanying questionnaire. These tools not only offer a deep understanding of the impact of military culture on individuals but also encapsulate a spectrum of values, attitudes, and behaviors prevalent in these male-dominated setups.

Through Zimbardo’s pioneering work, SIS serves as a lens to study the psychological dimensions of military socialization and the potential implications on the involved individuals.

Enduring Legacy of Dr. Philip Zimbardo

Philip Zimbardo’s illustrious career in psychology spans over five decades, leaving a lasting impression on the field that continues to shape both academic and public perceptions of the discipline. His enduring influence is particularly evident in his diverse roles as an educator, a researcher, and an advocate for social change.

Zimbardo is a tireless proponent for the spread of psychological knowledge. His fervor for teaching is palpable in his career as an educator, which has lasted for over half a century. Demonstrating his commitment to ‘give psychology away,’ Zimbardo has undertaken numerous efforts to make the field more accessible to the general public. His PBS-TV series, ‘Discovering Psychology,’ and his textbook, ‘Psychology and Life,’ have played a crucial role in demystifying psychology for the layperson.

In the realm of research, Zimbardo’s contributions to social psychology are impressive. His studies on police interrogation tactics, vandalism, and the prison system have provoked substantial changes to governmental policies. His groundbreaking 1971 Stanford Prison Experiment, remains a foundational aspect of social psychology, providing invaluable insights into the extent of human conformity and obedience to authority.

Zimbardo’s role as an advocate for social change is embodied in initiatives like the Harlem Summer Project, a program that offered educational opportunities to disadvantaged children. His patriotic dissent against various U.S. government policies, such as the Vietnam War and the Iraq War, further underscores his commitment to use psychology as a tool for social improvement.

In addition to his retirement plans, Dr. Philip Zimbardo has taken on a new role as executive director of the Center for Interdisciplinary Policy, Education, and Research on Terrorism (CIPERT) at Stanford University. CIPERT is a Stanford center focused on the study of terrorism. By becoming CIPERT’s executive director, Zimbardo adds leadership of the terrorism research center to his list of activities in retirement.

Beyond his academic achievements, Zimbardo’s legacy is also marked by his philanthropic endeavors. His charitable foundation supports student education in his ancestral towns in Sicily. Altogether, Zimbardo’s significant legacy in psychology is a testament to his steadfast dedication to advancing the field and enhancing human well-being.

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Philip Zimbardo (Biography + Experiments)

Who Is Philip Zimbardo?

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

Philip Zimbardo Short Biography

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

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

What is The Stanford Prison Experiment?

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

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

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

Stanford Prison Experiment Method

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

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

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

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

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

Rules of the Study

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

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

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

Results of the Stanford Prison Experiment

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

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

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

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

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

Increasing Cruelty

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

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

All In on the Experiment 

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

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

Solitary Confinement

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

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

Why Did the Stanford Prison Experiment End Early?

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

Conclusions from the Stanford Prison Experiment

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

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

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

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

Criticism and Limitations of The Stanford Prison Experiment

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

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

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

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

Replications of Stanford Prison Experiment 

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

Zimbardo’s Other Interests, Contributions, and Awards

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

Haney, C. & Zimbardo, P. (1998). The past and future of u.s. prison policy: Twenty-five years after the stanford prison experiment. American Psychologist, 53 (7) , 709-727. Retrieved from https://www.gvsu.edu/cms4/asset/F51281F0-00AF-E25A-5BF632E8D4A243C7/stanford_prison_experiment.pdf

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

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

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

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

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Dr. Philip Zimbardo on What Really Happened During the Stanford Prison Experiment

Asking the lead researcher about his infamy, and about the new cinematic version of his experiment.  

On a mid-August morning in the late summer of 1971, Palo Alto police cars were spread across the city picking up a predetermined number of college students throughout the small California town. They were arrested for armed robbery or burglary, booked and fingerprinted at the local police station, blindfolded, and then swiftly brought to the nearby Stanford County Prison. It was a harrowing scene, but none of it was real. Until it was.

The students picked up that day were willing participants in the Stanford Prison Experiment , perhaps the most infamous study in the history of social psychology. In it, 18 students were randomly selected to assume the roles of prisoners or guards and to be monitored 24/7 at a fake prison in the basement of Stanford University’s Jordan Hall, under the supervision of lead psychologist and professor Philip Zimbardo, who acted as the prison’s “superintendent.” All participants would be paid a then-significant sum of $15 per day.

The guards, given little instruction on how to manage the prisoners, eventually started psychologically and then physically abusing the prisoners a mere day after the study began, at which point the study devolved into an extreme, unrestrained Lord of the Flies -type situation. Zimbardo, 38 at the time, and his cohort remained willing bystanders to the increasingly depraved behavior. The experiment was scheduled to last two weeks, but was abruptly cancelled after only six days.

It’s now the subject of a new film to be released this week — a dramatic re-telling and not a documentary — called The Stanford Prison Experiment , and it brings to light once more the controversial gray areas surrounding what happened and the polarizing figurehead behind it all: Zimbardo himself, who has been involved in bringing the story of the experiment to the silver screen for decades. “There have been many scripts, many iterations,” Zimbardo told me when I met with him to talk about the study and the new movie. “I’ve been working on this film for 35 years.”

For better or worse, Zimbardo is an opportunist first and an educator second, who has ridden the prison experiment’s notoriety for the rest of his career. Though according to him there was “zero” fallout from the experiment immediately after it was ended, its scientific intentions using a group of innocent kids gave way to an unethical but revealing conclusion about human nature that gained fame following a series of actual prison riots at San Quentin and Attica in the 1970s.

He is a personable, sometimes kooky, presence and carries the air of a P.T. Barnum-esque showman. He also legitimately believes in the worth of what happened — despite the fact that it was totally unethical and could never be rightfully recreated, except in a movie like this.

Zimbardo (right) and actor Billy Crudup, who portrays him in the film

Yet during our interview he was willing to admit fault. “I was gradually being transformed by my role of prison superintendent. That was the big mistake,” he said. “I should have had somebody else do that.” He says his personal involvement and the problems that arose weren’t all on him. “The other problem was as a researcher I seriously underestimated the size of a team you need to run this kind of research. It was four people: me, two graduate students, and an undergrad.”

When one of the team dropped out, three people — including Zimbardo — were working around the clock to supervise each of the 12 people in the experiment at a given time. “We were all over-stressed, and unaware,” he said. “I was trapped in the experiment.”

This sort of sentiment typifies Zimbardo’s relationship to what happened. He understands that what went down under his supervision was bad, even realizing it during the experiment itself. Yet he was the one who fostered the behavior of the allegedly autonomous guards to make it that way. Everything that went wrong with the experiment can be traced to his influence, even his instructions.

Carlo Prescott, the former San Quentin prisoner who helped Zimbardo and his team create the Stanford Prison’s atmosphere, questioned the experiment in retrospect , “How can Zimbardo … express horror at the behavior of the ‘guards’ when they were merely doing what Zimbardo and others, myself included, encouraged them to do at the outset or frankly established as ground rules?” Later, he defeatedly said: “I blew it. I became an unwitting accomplice to a theatrical exercise that conveniently absolves all comers of personal responsibility for their abominable moral choices.

John Mark, one of the “guards,” told the Stanford Alumni magazine in 2011 what he thought of Zimbardo’s contradictions, “Throughout the experiment, he knew what he wanted and then tried to shape the experiment — by how it was constructed, and how it played out — to fit the conclusion that he had already worked out.”

These statements point out one of the main criticisms that have been leveled at Zimbardo as the experiment has gained its infamy over the years: Could these normal, healthy kids have had an innate ability to become monsters, or was there something — or someone — influencing them?

Boston College professor Peter Gray posed this question in Psychology Today magazine, “What would have happened if Zimbardo had said to the guards, at the outset, that the purpose of the experiment was to prove that it is possible to be both a guard and a decent human being, or in some way implied that the goal was to prove that guards can be kind?”

It becomes obvious that by being involved, Zimbardo may have willingly steered the experiment towards its controversial end.

Gray also put his criticism more succinctly, “This is a study of prisoners and guards, so their job clearly is to act like prisoners and guards — or, more accurately, to act out their stereotyped views of what prisoners and guards do,” he said. “Surely, Professor Zimbardo, who is right there watching them (as the Prison Superintendent) would be disappointed if, instead, they had just sat around chatting pleasantly and having tea.”

Zimbardo himself admitted to me that had things not escalated, the study would have ended. “At the end of day one I said, ‘Forget it, nothing is happening.’” But as soon as the prisoners began fighting back against the cruel behavior, which escalated into a nine person mini-riot , he knew he had something. “Literally, if the revolt had not happened, I would have ended the second day and said ‘There’s nothing here.’”

Zimbardo, who acted as a consultant on the film, gladly defends its narrative against what really happened. “I’d say the movie itself is a very faithful rendition of the Stanford Prison Experiment as it happened,” he said. “I would say if you had to give a number it’s about 90 percent right-on. There are a few places where obviously the director took poetic license, but all the dialogue [in the film] between prisoners and guards is exactly what happened.”

To him, the best reason to make a fictional film out of the experiment is to educate and to find some sort of legitimate point of view from these mistakes. Though a recent study found that out of 13 introductory psychology textbooks that mentioned the experiment, only six explained its less than proper methods. Despite the fact that there are relative treasure troves of source materials about the experiment available (you can start with Stanford’s own collection here ), maybe the movie will allow more people than ever to decide for themselves how wrong or how right it was.

I asked him why he didn’t stop the experiment when it escalated out of control. “That, I feel guilty about,” he said. “That is a mistake. But again, it’s a testimony to what the experiment was trying to demonstrate. It’s the power of situations to overwhelm good intentions, moral conscious, and character in kids but also sophisticated grownups.” Then he added, “And I feel guilty and sorry about that.”

Zimbardo himself continues to somewhat reluctantly benefit from its infamy, especially when situations like the Abu Ghraib prison scandal add more credence to the experiment’s psychological truths. The movie is worth seeing simply to get a sense of how all this craziness went down and as a reminder of how situational your ethics may truly be.

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The Influence of Philip Zimbardo on Psychology

• Career and Research

Notable Publications

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Frequently Asked Questions

Philip Zimbardo is an influential psychologist best-known for his 1971 Stanford Prison Experiment . Many psychology students may also be familiar with his introductory psychology textbooks and Discovering Psychology video series, which are often used in high school and psychology classrooms. He is also known for his research on shyness. Zimbardo is the author of several notable books including The Lucifer Effect: Understanding How Good People Turn Evil.

Zimbardo has also conducted important research on the psychology of heroism and is the founder of the Heroic Imagination Project , a non-profit organization aimed at understanding and promoting everyday heroism .

His Early Life

Philip Zimbardo was born on March 23, 1933, in New York City. He attended Brooklyn College where he earned a BA in 1954, triple majoring in psychology, sociology, and anthropology. He then went on to earn his MS in 1955 and his PhD in 1959 from Yale University, both in psychology.

He taught briefly at Yale before becoming a psychology professor at New York University, where he taught until 1967. After a year of teaching at Columbia University, he became a faculty member at Stanford University in 1968, where he worked until his retirement in 2003. He delivered his final lecture at Stanford in 2007.

Zimbardo's Career and Research

Zimbardo's career has spanned decades and covered a wide variety of subjects, from social conformity to shyness to military socialization.

Stanford Prison Experiment

Philip Zimbardo is perhaps best known for the Stanford Prison Experiment, conducted in the basement of the Stanford University psychology department in 1971. The participants in the study were 24 male college students who were randomly assigned to act either as "guards" or "prisoners" in the mock prison.

The study was initially slated to last two weeks but had to be terminated after just six days because of the extreme reactions and behaviors of the participants. The guards began displaying cruel and sadistic behavior toward the prisoners, while the prisoners became depressed and hopeless.

While the study is a staple of psychology textbooks and its events portrayed in a feature film, recent findings indicate that the experiment lacked credibility and authenticity. In an exposé titled "The Lifespan of a Lie," journalist Ben Blum reported that the experimenters intentionally influenced the experiment and the results.

Zimbardo Time Perspective Inventory (ZTPI)

Zimbardo also developed an inventory to measure time perspective, which is believed to significantly influence human behavior. It includes people's views of past, current, and future behavior.

Social Intensity Syndrome (SIS)

Zimbardo also developed a social intensity syndrome (SIS) theory to describe how military culture and socialization affect soldiers and military veterans. Research has demonstrated that the construct is an accurate measure of military socialization. Zimbardo and his colleagues suggest that SIS may be an important way to gain better insight into military culture's positive and negative effects.

The Shyness Clinic

Zimbardo has also researched the effects of shyness and how it can be treated in both children and adults. He established The Shyness Clinic, located in Palo Alto, California, to research traits associated with shyness and provide treatment for shy behaviors, primarily through practicing social skills and engaging in social activities.

"Psychology of Evil" TED Talk

In 2008, Zimbardo delivered a TED Talk on the psychology of evil. He summarized research on evil, discussed how these insights explained the atrocities at Abu Ghraib, and how people can practice heroism in their everyday lives.

Heroic Imagination Project

Today, he continues to work as the director of the Heroic Imagination Project . The organization promotes research, education and media initiatives designed to inspire ordinary people to act as heroes and agents of social change.

Zimbardo has published a number of books, textbooks, and journal articles throughout his career. Some of the most notable include:

The Lucifer Effect

Zimbardo's 2007 book included his account of the events of the 1971 Standford Prison Experiment. The book explored why people sometimes do bad things and how people cross the line from good to evil, often without realizing what they have done.

The Time Paradox

In "The Time Paradox: The New Psychology of Time That Will Change your Life," Zimbardo and his co-author John Boyd explored how people's attitudes toward time shape their behaviors and decisions. It also explored how distorted perceptions of time can contribute to mental health problems.

The Time Cure

In this book, Zimbardo and his co-authors Richard and Rosemary Sword take the concept of time perspective and apply it to the treatment of post-traumatic stress disorder (PTSD). By shifting how people think about time, Zimbardo and his colleagues suggested, people can better move past the trauma they have experienced.

Zimbardo's most recent publication is the 2015 book "Man (Dis)connected: How Technology Has Sabotaged What It Means To Be Male."

His Contributions to Psychology

Philip Zimbardo’s Stanford Prison Experiment has long served as an example of how situational forces influence human behavior. The study became a topic of interest after the reports of the Abu Ghraib prisoner abuses in Iraq became public knowledge. Many people, Zimbardo included, suggested that the abuses at Abu Ghraib might be real-world examples of the same results observed in Zimbardo's experiment.

Since the famous prison experiment, Zimbardo has researched various topics, including shyness, cult behavior, and heroism. He has authored and co-authored numerous books some people may recognize him as the host of the Discovering Psychology video series, which has aired on PBS and is often used in high school and college psychology classes.

In 2002, Zimbardo was elected president of the American Psychological Association . After more than 50 years of teaching, Zimbardo retired from Stanford in 2003 but gave his last "Exploring Human Nature" lecture on March 7, 2007.

Zimbardo has also served as an influential figure in psychology through his writings as well as his long teaching career.

A Word From Verywell

While Zimbardo's best-known experiment took place decades ago, its impact is still felt on psychology today. The images of torture and prisoner abuse that emerged from the Iraq prison known as Abu Ghraib echoed the notorious events in Zimbardo's infamous experiment.

The Stanford Prison Experiment has long been one of the most famous experiments in psychology. However, it has long been criticized for its ethical problems and, more recently, its scientific credibility has been called into question.

Zimbardo is now 89 years old. He retired from teaching at Stanford after a 50-year career but continues to work as the director of the Heroic Imagination Project, the organization he founded to explore the psychology of everyday heroism.

Recent critiques have called the Stanford Prison Experiment's scientific credibility into question. In addition to the problematic ethical concerns with the research, new examinations suggest the experimenters intentionally encouraged the abusive behavior of the prison guards. A 2019 article published in American Psychologist debunked the famous experiment, declaring the study both deeply flawed and unworthy of the attention it has commanded for decades.  

Zimbardo suggested that there are five different time perspectives:  

• Past-positive perspective involves positive evaluations of the past. 
• Past-negative perspective involves negatively evaluating the past. 
• Future-perspective involves goal-based thinking about the future.
• Present-hedonistic perspective involves focusing on finding pleasure in the present moment.
• Present- fatalistic perspective involves existing passively in the present and believing that events are fated or pre-destined.

Zimbardo P, Haney C, Banks WC, Jaffe D.  The Stanford Prison Experiment: A simulation study of the psychology of imprisonment . Stanford University, Stanford Digital Repository, Stanford.

American Psychological Association. Philip G. Zimbardo: 2002 APA President .

American Psychological Association. Demonstrating the power of social situations via a simulated prison experiment .

Blum B. The lifespan of a lie .

Peng C, Yue C, Avitt A, Chen Y. A systematic review approach to find robust items of the Zimbardo time perspective inventory . Front Psychol . 2021;12:627578. doi:10.3389/fpsyg.2021.627578

Zimbardo PG, Ferreras AC, Brunskill SR. Social intensity syndrome: The development and validation of the social intensity syndrome scale . Personality and Individual Differences . 2015;73:17-23. doi:10.1016/j.paid.2014.09.014

TED. The psychology of evil .

American Psychological Association. Psychological science offers clues to Iraqi prisoner abuse .

Stanford University. About Philip G. Zimbardo .

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

Sobol-Kwapińska M, Jankowski T, Przepiorka A, Oinyshi I, Sorokowski P, Zimbardo P. What is the structure of time? A study on time perspective in the United States, Poland, and Nigeria . Front Psychol . 2018;9:2078. doi:10.3389/fpsyg.2018.02078

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

Biography of Philip Zimbardo

The Legacy of His Famous "Stanford Prison Experiment"

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

Early Life and Education

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

The Stanford Prison Study

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

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

The Prison Experiment’s Impact

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

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

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

Critiques of the Prison Experiment

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

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

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

Other Work by Zimbardo

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

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

Recent Research: Understanding Heroes

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

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

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

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

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

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

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

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