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Prison Guard Experiment Stanford Case Study

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

This article is about the psychology experiment. For the American punk pop band, see Stanford Prison Experiment (band). For the 2015 film, see The Stanford Prison Experiment (film).

"Stanford experiment" redirects here. For the experiment on delayed gratification, see Stanford marshmallow experiment.

The Stanford prison experiment (SPE) was an attempt to investigate the psychological effects of perceived power, focusing on the struggle between prisoners and prison officers. It was conducted at Stanford University between August 14–20, 1971, by a research group led by psychology professor Philip Zimbardo using college students.[1] It was funded by the U.S. Office of Naval Research[2] as an investigation into the causes of difficulties between guards and prisoners in the United States Navy and United States Marine Corps. The experiment is a topic covered in most introductory (social) psychology textbooks.[3]

Guards and prisoners had been chosen randomly from the volunteering college students. Some participants developed their roles as the officers and enforced authoritarian measures and ultimately subjected some prisoners to psychological torture. Many of the prisoners passively accepted psychological abuse and, by the officers' request, actively harassed other prisoners who tried to stop it. Zimbardo, in his role as the superintendent, allowed abuse to continue.[4][5] Two of the prisoners left mid-experiment, and the whole exercise was abandoned after six days following the objections of graduate student Christina Maslach, whom Zimbardo was dating (and later married). Certain portions of the experiment were filmed, and excerpts of footage are publicly available.

Goals and methods[edit]

Zimbardo and his team aimed to test the hypothesis that the inherent personality traits of prisoners and guards are the chief cause of abusive behavior in prison. Participants were recruited and told they would participate in a two-week prison simulation. The team selected the 24 males whom they deemed to be the most psychologically stable and healthy.[6] These participants were predominantly white[7] and of the middle class.[8] The group was intentionally selected to exclude those with criminal backgrounds, psychological impairments, or medical problems. They all agreed to participate in a 7- to 14-day period and received $15 per day (approximately $90 in 2017).[9]

The experiment was conducted in a 35-foot (10.5 m) section of a basement of Jordan Hall (Stanford's psychology building). The prison had two fabricated walls, one at the entrance, and one at the cell wall to block observation. Each cell (6 × 9 feet, or 1.8 × 2.7 m), contained only a cot for the prisoners.[10] In contrast, the guards lived in a very different environment, separated from the prisoners. They were given rest and relaxation areas, and other comforts.

Twelve of the 24 participants were assigned the role of prisoner (9 plus 3 alternates), while the other 12 were assigned the role of guard (also 9 plus 3 alternates). Zimbardo took on the role of the superintendent, and an undergraduate research assistant the role of the warden. Zimbardo designed the experiment in order to induce disorientation, depersonalization, and deindividuation in the participants.

The researchers held an orientation session for guards the day before the experiment, during which guards were instructed not to physically harm the prisoners or withhold food or drink. In the footage of the study, Zimbardo can be seen talking to the guards: "You can create in the prisoners feelings of boredom, a sense of fear to some degree, you can create a notion of arbitrariness that their life is totally controlled by us, by the system, you, me, and they'll have no privacy ... We're going to take away their individuality in various ways. In general what all this leads to is a sense of powerlessness. That is, in this situation we'll have all the power and they'll have none."[11]

The researchers provided the guards with wooden batons to establish their status,[12] clothing similar to that of an actual prison guard (khaki shirt and pants from a local military surplus store), and mirrored sunglasses to prevent eye contact. Prisoners wore uncomfortable, ill-fitting smocks and stocking caps, as well as a chain around one ankle. Guards were instructed to call prisoners by their assigned numbers, sewn on their uniforms, instead of by name.

The prisoners were "arrested" at their homes and "charged" with armed robbery. The local Palo Alto police department assisted Zimbardo with the arrests and conducted full booking procedures on the prisoners, which included fingerprinting and taking mug shots. The prisoners were transported to the mock prison from the police station, where they were strip searched and given their new identities.

The small mock prison cells were set up to hold three prisoners each. There was a small corridor for the prison yard, a closet for solitary confinement, and a bigger room across from the prisoners for the guards and warden. The prisoners were to stay in their cells and the yard all day and night until the end of the study. The guards worked in teams of three for eight-hour shifts. The guards were not required to stay on site after their shift.


After a relatively uneventful first day, on the second day the prisoners in Cell 1 blockaded their cell door with their beds and took off their stocking caps, refusing to come out or follow the guards' instructions. Guards from other shifts volunteered to work extra hours, to assist in subduing the revolt, and subsequently attacked the prisoners with fire extinguishers without being supervised by the research staff. Finding that handling nine cell mates with only three guards per shift was challenging, one of the guards suggested they use psychological tactics to control them. They set up a "privilege cell" in which prisoners who were not involved in the riot were treated with special rewards, such as higher quality meals. The "privileged" inmates chose not to eat the meal in commiseration with their fellow prisoners.

After only 36 hours, one prisoner began to act "crazy", as Zimbardo described: "#8612 then began to act crazy, to scream, to curse, to go into a rage that seemed out of control. It took quite a while before we became convinced that he was really suffering and that we had to release him." Guards forced the prisoners to repeat their assigned numbers[13] to reinforce the idea that this was their new identity. Guards soon used these prisoner counts to harass the prisoners, using physical punishment such as protracted exercise for errors in the prisoner count. Sanitary conditions declined rapidly, exacerbated by the guards' refusal to allow some prisoners to urinate or defecate anywhere but in a bucket placed in their cell. As punishment, the guards would not let the prisoners empty the sanitation bucket. Mattresses were a valued item in the prison, so the guards would punish prisoners by removing their mattresses, leaving them to sleep on concrete. Some prisoners were forced to be naked as a method of degradation. Several guards became increasingly cruel as the experiment continued; experimenters reported that approximately one-third of the guards exhibited genuine sadistic tendencies. Most of the guards were upset when the experiment was halted after only six days.

Zimbardo mentions his own absorption in the experiment. On the fourth day, some of the guards stated they heard a rumor that the released prisoner was going to come back with his friends and free the remaining inmates. Zimbardo and the guards disassembled the prison and moved it onto a different floor of the building. Zimbardo himself waited in the basement, in case the released prisoner showed up, and planned to tell him that the experiment had been terminated. The released prisoner never returned, and the prison was rebuilt in the basement.

Zimbardo argued that the prisoners had internalized their roles, since some had stated they would accept "parole" even if it would mean forfeiting their pay, despite the fact that quitting would have achieved the same result without the delay involved in waiting for their parole requests to be granted or denied.[14] Zimbardo argued they had no reason for continued participation in the experiment after having lost all monetary compensation, yet they did, because they had internalized the prisoner identity.

Prisoner No. 416, a newly admitted stand-by prisoner, expressed concern about the treatment of the other prisoners. The guards responded with more abuse. When he refused to eat his sausages, saying he was on a hunger strike, guards confined him to "solitary confinement", a dark closet: "the guards then instructed the other prisoners to repeatedly punch on the door while shouting at 416."[15] The guards said he would be released from solitary confinement only if the prisoners gave up their blankets and slept on their bare mattresses, which all but one refused to do.

Zimbardo aborted the experiment early when Christina Maslach, a graduate student in psychology whom he was dating (and later married),[16] objected to the conditions of the prison after she was introduced to the experiment to conduct interviews. Zimbardo noted that, of more than 50 people who had observed the experiment, Maslach was the only one who questioned its morality. After only six days of a planned two weeks' duration, the experiment was discontinued.[14]


On August 20, 1971, Zimbardo announced the end of the experiment to the participants.

The experiment's results favor situational attribution of behavior over dispositional attribution (a result caused by internal characteristics). It seemed that the situation, rather than their individual personalities, caused the participants' behavior. Using this interpretation, the results are compatible with those of the Milgram experiment, where random participants complied with orders to administer seemingly dangerous and potentially lethal electric shocks to a shill.[17]

The experiment has also been used to illustrate cognitive dissonance theory and the power of authority.

Shortly after the study was completed, there were bloody revolts at both the San Quentin and Attica prison facilities, and Zimbardo reported his findings on the experiment to the U.S. House Committee on the Judiciary.

Participants' behavior was modified due to the fact that they were watched as opposed to a lurking variable (Hawthorne effect).[18] Even knowing they were being observed, guards and prisoners acted differently than normal. Some guards felt the need to show their dominance even when it was not necessary.[citation needed]

Zimbardo instructed the guards before the experiment to disrespect the prisoners in various ways. For example, they had to refer to prisoners by number rather than by name. This, according to Zimbardo, was intended to diminish the prisoners' individuality.[19] With no control, prisoners learned they had little effect on what happened to them, ultimately causing them to stop responding, and give up.[10] Quick to realize that the guards were the highest in the hierarchy, prisoners began to accept their roles as less important human beings.

The uniforms were given to all participants to erase individual identity, and participants were randomly chosen to be either a prisoner or guard to reduce individuality.[10]

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.[18]


Some of the guards' behaviour led to dangerous and psychologically damaging situations. One third of the guards were judged to have exhibited "genuine sadistic tendencies", while many prisoners were emotionally traumatized; five of them had to be removed from the experiment early. After Maslach confronted Zimbardo and forced him to realize that he had been passively allowing unethical acts to be performed under his supervision, Zimbardo concluded that both prisoners and guards had become grossly absorbed in their roles and realized that he had likewise become as grossly absorbed in his own, and he terminated the experiment.[20] Ethical concerns surrounding the experiment often draw comparisons to a similar experiment, conducted ten years earlier in 1961 at Yale University by Stanley Milgram.[17]

Because of the nature and questionable ethics of the experiment, Zimbardo found it impossible to keep traditional scientific controls in place. He was unable to remain a neutral observer, since he influenced the direction of the experiment as the prison's superintendent. Conclusions and observations drawn by the experimenters were largely subjective and anecdotal, and the experiment is practically impossible for other researchers to accurately reproduce. Erich Fromm claimed to see generalizations in the experiment's results and argued that the personality of an individual does affect behavior when imprisoned. This ran counter to the study's conclusion that the prison situation itself controls the individual's behavior. Fromm also argued that the amount of sadism in the "normal" subjects could not be determined with the methods employed to screen them.[citation needed]

"John Wayne" (the real-life Dave Eshelman), one of the guards in the experiment, said the study placed undue emphasis on the cruelty of the guards, and that he caused the escalation of events between guards and prisoners after he began to emulate a character from the 1967 film Cool Hand Luke. He further intensified his actions because he was nicknamed "John Wayne" by the other participants, even though he was trying to mimic actor Strother Martin, who had played the role of the sadistic prison Captain in the movie.[21]

What came over me was not an accident. It was planned. I set out with a definite plan in mind, to try to force the action, force something to happen, so that the researchers would have something to work with. After all, what could they possibly learn from guys sitting around like it was a country club? So I consciously created this persona. I was in all kinds of drama productions in high school and college. It was something I was very familiar with: to take on another personality before you step out on the stage. I was kind of running my own experiment in there, by saying, "How far can I push these things and how much abuse will these people take before they say, 'knock it off?'" But the other guards didn't stop me. They seemed to join in. They were taking my lead. Not a single guard said, "I don't think we should do this." ―David Eshelman[22]

Also, researchers from Western Kentucky University argued that selection bias may have played a role in the results. The researchers recruited students for a study using an advertisement similar to the one used in the Stanford Prison Experiment, with some ads saying "a psychological study" (the control group), and some with the words "prison life" as originally worded in Dr. Zimbardo's Stanford Prison Experiment. It was found that students who responded to the classified advertisement for the "prison study" were higher in traits such as social dominance, aggression, authoritarianism, etc. and were lower in traits related to empathy and altruism when statistically compared to the control group participants.[23]

The study has been criticized for demand characteristics by psychologist Peter Gray. He argues that participants in psychological experiments are more likely to do what they believe the researchers want them to do. The guards were essentially told to be cruel. However, it could be argued that it was precisely this willingness to comply with the experiment's questionable practices that showed how little was needed for the students to engage in such practices.[24]

Skeptical author Brian Dunning states:

Most of the Stanford guards did not exhibit any cruel or unusual behavior, often being friendly and doing favors for the prisoners...The statistical validity of the sample of participants, 24 male Stanford students of about the same age, has been called into question as being too small and restrictive to be generally applicable to the population at large...(and the fact that) Zimbardo has dedicated much of his career to the promotion of the idea that bad environments drive bad behavior.[25]

Guards and prisoners were playing the role of their authority, which is subjective.[18] They may have not acted the same in real life situations. In particular, the environment and authority roles they found themselves in changed their actions.

Critics contend that not only was the sample size too minimal for extrapolation, but also having all of the experimental subjects be US male students gravely undercut the experiment's validity. In other words, it's entirely conceivable that replicating the experiment using a diverse group of people (with different objectives and views in life)[18] would have produced radically distinct results; that is, had the test subjects come from divergent socio-economic and psychological groups, different experimental results may well have resulted.

Comparisons to Abu Ghraib[edit]

When acts of prisoner torture and abuse at the Abu Ghraib prison in Iraq were publicized in March 2004, Zimbardo himself, who paid close attention to the details of the story, was struck by the similarity with his own experiment. He was dismayed by official military and government representatives' shifting the blame for the torture and abuses in the Abu Ghraib American military prison onto "a few bad apples" rather than acknowledging the possibly systemic problems of a formally established military incarceration system.

Eventually, Zimbardo became involved with the defense team of lawyers representing one of the Abu Ghraib prison guards, Staff Sergeant Ivan "Chip" Frederick. He was granted full access to all investigation and background reports, and testified as an expert witness in SSG Frederick's court martial, which resulted in an eight-year prison sentence for Frederick in October 2004.

Zimbardo drew from his participation in the Frederick case to write the book The Lucifer Effect: Understanding How Good People Turn Evil, published by Random House in 2007, which deals with the striking similarities between his own Stanford Prison Experiment and the Abu Ghraib abuses.[15]

Ethical issues[edit]

The experiment was perceived by many to involve questionable ethics, the most serious concern being that it was continued even after participants expressed their desire to withdraw. Despite the fact that participants were told they had the right to leave at any time, Zimbardo did not allow this during the experiment.[18] Zimbardo was faced with the ethical dilemma that the experiment could possibly return outstanding results if continued, but it might also adversely affect the participants' well-being if not halted.

Since the time of the Stanford experiment, ethical guidelines have been established for experiments involving human subjects. [26][27][28] The Stanford Prison Experiment led to the implementation of rules to preclude any harmful treatment of participants. Before they are implemented, human studies must now be reviewed and found by an institutional review board (US) or ethics committee (UK) to be in accordance with ethical guidelines set by the American Psychological Association.[18] These guidelines involve consideration of whether the potential benefit for science outweighs the possible risk for physical and psychological harm.

A post-experimental debriefing is now considered an important ethical consideration to ensure that participants are not harmed in any way by their experience in an experiment. Though Zimbardo did conduct debriefing sessions, they were several years after the Stanford Prison Experiment. By that time numerous details were forgotten; nonetheless, many participants reported that they experienced no lasting negative effects.[18] Current standards specify that the debriefing process should occur as soon as possible to assess what psychological harm, if any, may have been done and to rehabilitate participants, if necessary. If there is an unavoidable delay in debriefing, the researcher is obligated to take steps to minimize harm.[29]

Similar studies[edit]

BBC prison study[edit]

Psychologists Alex Haslam and Steve Reicher conducted the BBC Prison Study in 2002 and published the results in 2006.[30] This was a partial replication of the Stanford prison experiment conducted with the assistance of the BBC, which broadcast events in the study in a documentary series called The Experiment. Their results and conclusions differed from Zimbardo's and led to a number of publications on tyranny, stress, and leadership. The results were published in leading academic journals such as British Journal of Social Psychology, Journal of Applied Psychology, Social Psychology Quarterly, and Personality and Social Psychology Review. The BBC Prison Study is now taught as a core study on the UK A-levelPsychology OCR syllabus.

While Haslam and Reicher's procedure was not a direct replication of Zimbardo's, their study casts further doubt on the generality of his conclusions. Specifically, it questions the notion that people slip mindlessly into role and the idea that the dynamics of evil are in any way banal. Their research also points to the importance of leadership in the emergence of tyranny of the form displayed by Zimbardo when briefing guards in the Stanford experiment.[31][32]

Experiments in the United States[edit]

The Stanford prison experiment was in part a response to the Milgram experiment at Yale beginning in 1961 and published in 1963.[33]

The Third Wave experiment involved the use of authoritarian dynamics similar to Nazi Party methods of mass control in a classroom setting by high school teacher Ron Jones in Palo Alto, California, in 1976 with the goal of demonstrating to the class in a vivid way how the German public in World War II could have acted in the way it did.[34] Although the veracity of Jones' accounts has been questioned,[35][unreliable source?] several participants in the study have gone on record to confirm the events.[36]

In both experiments, participants found it difficult to leave the study due to the roles they were assigned. Both studies examine human nature and the effects of authority. Personalities of the subjects had little influence on both experiments despite the test prior to the prison experiment.[37]

In the Milgram and the Zimbardo studies, participants conform to social pressures. Conformity is strengthened by allowing some participants to feel more or less powerful than others.[37] In both experiments, behavior is altered to match the group stereotype.

In popular culture[edit]

  • American science fiction writer Gene Wolfe published a story, When I was Ming the Merciless (1975), inspired by the Stanford Prison Experiment. In the story, college student volunteers are randomly assigned to factions (Blue, Green, and Yellow) and locked in a campus building. Violence ensues.[38]
  • In 1977, Italian director Carlo Tuzii adapted the experiment to an Italian environment. Italian students made a film based on it, La Gabbia (The Cage).
  • Quiet Rage: The Stanford Prison Experiment (1992), is a documentary about the experiment, made available via the Stanford Prison Experiment website. The documentary was written by Zimbardo and directed and produced by Ken Musen.[39]
  • The novel Black Box, written by Mario Giordano and inspired by the experiment, was adapted for the screen by German director Oliver Hirschbiegel as Das Experiment (2001).
  • In the third season of the television series Veronica Mars (2006–2007), a variant of the experiment is recreated as an activity for a sociology class, the main difference being that the guards were expected to get information out of the prisoners.
  • In an October 2008 episode of the NBC television show Life, Detectives Crews and Reese investigated a murder that took place at a prison experiment loosely modeled on the Stanford Prison Experiment.
  • The 2010 film The Experiment is an English-language remake of the 2001 film Das Experiment.
  • The Japanese serialized manga Prison School, first published in February 2011, heavily references the Stanford Prison Experiment as the inspiration for Kate's revenge plot.
  • Broadening, a play in the 2012 Dublin Fringe Festival, was based on the Stanford experiment.
  • The experiment was featured in a 2012 episode of Science's Dark Matters: Twisted But True in the documentary short "Creative Evil".
  • In 2014, the Danish national television channel DR3 recreated the experiment in the television series Ond, ondere, ondest.
  • The 2015 film The Stanford Prison Experiment is another film based on the experiment.[40]
  • "PhDead" episode 154 of the TV series Castle, season 8 (air date: October 5, 2015): Castle and Beckett investigate a murder and discover its relationship to a recreation of the Stanford Prison Experiment.
  • In an October 2015 episode of the ITV television show Lewis, the second half mentions the Stanford prison experiment, and eventually the whole case revolves around it.
  • In a December 2017 episode of the YouTube Red series Mind Field, Zimbardo discusses the experiment with host Michael Stevens with regards to what defines a hero.

See also[edit]


  1. ^The Stanford Prison Experiment – A Simulation Study of the Psychology of Imprisonment Conducted at Stanford University
  2. ^FAQ on official site
  3. ^Intro to psychology textbooks gloss over criticisms of Zimbardo's Stanford Prison Experiment
  4. ^Beyond Ethics to Post-ethics: A Preface to a New Theory of Morality and Immorality, Peter Baofu
  5. ^The Successes and Failures of Whistleblower Laws, Robert G. Vaughan
  6. ^Smith, J. R.; Haslam, S. A., eds. (2012). Social Psychology: Revisiting the Classic Studies. Sage. 
  7. ^Saletan, William (2004-05-12). "Situationist Ethics". Slate. ISSN 1091-2339. Retrieved 2016-02-02. 
  8. ^"Slideshow on official site". Prisonexp.org. p. Slide 4. 
  9. ^Haney, C.; Banks, W. C.; Zimbardo, P. G. (1973). "Interpersonal dynamics in a simulated prison". International Journal of Criminology and Penology. 1: 69–97.
  10. ^ abc"Index of /downloads". www.zimbardo.com. Archived from the original on January 20, 2015. Retrieved 2015-11-11. 
  11. ^"C82SAD L07 Social Influence II The BBC Prison Experiment (handout)". Psychology.nottingham.ac.uk. 
  12. ^Haney, C.; Banks, W. C. & Zimbardo, P. G. (1973). "Research reviews"(PDF). Zimbardo.com. 
  13. ^"Slide tour". The Stanford Prison Experiment. 
  14. ^ abZimbardo, P.G. (2007). The Lucifer Effect: Understanding How Good People Turn Evil. New York: Random House. 
  15. ^ ab"The Lucifer Effect". lucifereffect.com. 
  16. ^"The Standard Prison Experiment". Stanford University News Service. 
  17. ^ abKonnikova, Maria (June 12, 2015). "The Real Lesson of the Stanford Prison Experiment". The New Yorker.
  18. ^ abcdefg"Zimbardo – Stanford Prison Experiment | Simply Psychology". www.simplypsychology.org. Retrieved 2015-11-11. 
  19. ^Zimbardo (2007), The Lucifer Effect , p.54.
  20. ^"Conclusion". Stanford Prison Experiment. 
  21. ^"'John Wayne' (name withheld) Interview: 'The Science of Evil'". Primetime: Basic Instincts. KATU. January 3, 2007. 
  22. ^Eshelman, David (July 2011). "The Menace Within". Stanford Alumni Magazine. 
  23. ^Carnahan, Thomas; Sam McFarland (2007). "Revisiting the Stanford prison experiment: could participant self-selection have led to the cruelty?"(PDF). Personality and Social Psychology Bulletin. 33 (5): 603–14. doi:10.1177/0146167206292689. PMID 17440210. 
  24. ^Gray, Peter (2013). "Why Zimbardo's Prison Experiment Isn't in My Textbook". Freedom to Learn blog. 
  25. ^Dunning, Brian (27 March 2008). "Skeptoid #102: What You Didn't Know about the Stanford Prison Experiment". Skeptoid. Retrieved 22 June 2017. 
  26. ^U.S. Department of Health & Human Services Code of Federal Regulations, Title 45, Part 46, Protection of Human Subjects
  27. ^The Belmont Report, Office of the Secretary, Ethical Principles and Guidelines for the Protection of Human Subjects of Research, The National Commission for the Protection of Human Subjects for Biomedical and Behavioral Research, April 18, 1979
  28. ^U.S. Department of Health and Human Services, The Nuremberg Code
  29. ^American Psychological Association (2017). Ethical Principles of Psychologists and Code of Conduct, Sec. 8.07. http://www.apa.org/ethics/code/
  30. ^The BBC Prison Study Official Site
  31. ^Interview of Alex Haslam at The Guardian
  32. ^Reicher, Steve; Haslam, Alex. "Learning from the Experiment". The Psychologist (Interview). Interview with Briggs, Pam. Archived from the original on 2009-02-21. 
  33. ^"Milgram Experiment | Simply Psychology". www.simplypsychology.org. Retrieved 2017-02-10. 
  34. ^Jones, Ron (1976). "The Third Wave". The Wave Home. Archived from the original on 2015-02-02. Retrieved 2016-12-03. 
  35. ^"several email exchanges with former students". Archived from the original on 2013-01-27. Retrieved 2016-12-03. 
  36. ^"A Look at the Original Students of The Third Wave and Their Teacher Ron Jones, 40 Years Later"
  37. ^ ab"Comparing Milgram's Obedience and Zimbardo's Prison Studies". PSY 101 – Introduction to Psychology by Jeffrey Ricker, Ph.D. Retrieved 2015-11-12. 
  38. ^Wolfe, Gene (1975). When I was Ming the Merciless. 
  39. ^"Quiet Rage: The Stanford Prison Experiment (1992 documentary)". Justice videos. 
  40. ^Highfill, Samantha (July 17, 2015). "Billy Crudup turns college students into prison guards in The Stanford Prison Experiment". Entertainment Weekly.


  • 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 (5): 603–614. doi:10.1177/0146167206292689. PMID 17440210. 
  • Griggs, R. A. (2014). "Coverage of the Stanford Prison Experiment in introductory psychology textbooks". Teaching of Psychology. 41: 195–203. doi:10.1177/0098628314537968. 
  • Haney, C., Banks, W. C., & Zimbardo, P. G. (1973). "Study of prisoners and guards in a simulated prison", Naval Research Reviews, 9, 1–17. Washington, DC: Office of Naval Research.
  • Haney, C.; Banks, W. C.; Zimbardo, P. G. (1973). "Interpersonal dynamics in a simulated prison". International Journal of Criminology and Penology. 1: 69–97. 
  • Haslam, S. A.; Reicher, S. D. (2003). "Beyond Stanford: questioning a role-based explanation of tyranny". Dialogue (Bulletin of the Society for Personality and Social Psychology). 18: 22–25. 
  • Haslam, S. A.; Reicher, S. D. (2006). "Stressing the group: social identity and the unfolding dynamics of responses to stress". Journal of Applied Psychology. 91: 1037–1052. doi:10.1037/0021-9010.91.5.1037. 
  • Haslam, S. A.; Reicher, S. D. (2012). "When prisoners take over the prison: A social psychology of resistance". Personality and Social Psychology Review. 16: 154–179. doi:10.1177/1088868311419864. 
  • Musen, K. & Zimbardo, P. G. (1991). Quiet rage: The Stanford prison study. Videorecording. Stanford, CA: Psychology Dept., Stanford University.
  • Reicher; Haslam, S. A. (2006). "Rethinking the psychology of tyranny: The BBC Prison Study". British Journal of Social Psychology. 45: 1–40. 
  • Zimbardo, P. G. (1971). "The power and pathology of imprisonment", Congressional Record (Serial No. 15, 1971-10-25). Hearings before Subcommittee No. 3, of the United States House Committee on the Judiciary, 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 (2007) Understanding How Good People Turn Evil. Interview transcript. Democracy Now!, March 30, 2007. Accessed 17 January 2015.
  • 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. 
  • Mcleod, S. (2008). Zimbardo – Standford Prison Experiment/Simply Psychology. Retrieved November 12, 2015
  • Ricker, J. (2011, November 25). Comparing Milgrams Obedience and Zimbardo's Prison Studies. Retrieved November 12, 2015

External links[edit]

  • Stanford Prison Experiment, a website with info on the experiment and its impact
  • Summary of the experiment
  • Interviews with guards, prisoners, and researchers in July/August 2011 Stanford Magazine
  • Zimbardo, P. (2007). From Heavens to Hells to Heroes. In-Mind Magazine.
  • The official website of the BBC Prison Study
  • The Experiment (IMDb)  —German movie (Das Experiment) from 2001 inspired by the Stanford Experiment
  • "The Lie of the Stanford Prison Experiment", The Stanford Daily (April 28, 2005), p. 4  —Criticism by Carlo Prescott, ex-con and consultant/assistant for the experiment
  • The Artificial Prison of the Human Mind Article with Comments.
  • Philip Zimbardo on Democracy Now! March 30 2007
  • Philip Zimbardo on The Daily Show, March 2007
  • BBC news article – 40 years on, with video of Philip Zimbardo
  • Philip G. Zimbardo Papers (Stanford University Archives)

Abu Ghraib and the experiment:

Plaque Dedicated to the Location of the Stanford Prison Experiment

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