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Everything You Know About the Stanford Prison Experiment Is Wrong

I n August 1971, at the tail end of summer break, the Stanford psychology professor Philip Zimbardo recruited two dozen male college students for what was advertised as “a psychological study of prison life.” The basement of a university building was transformed into a makeshift prison. Some of the young men were assigned to be prisoners; the others became guards. The study turned dark almost immediately, as guards drunk on power mocked, humiliated, and cruelly punished their charges. Prisoners had breakdowns. Zimbardo had to shut down the study, which was supposed to run for two weeks, after just six days. While the experiment had been egregiously unethical, it did prove that circumstances have the power to make normal people act like tyrants—or what Zimbardo has called “the power of the situation.” 

So goes the legend of the Stanford Prison Experiment, cemented over more than half a century with lots of help from pop culture. Rocketed to fame when the Attica prison uprising dominated headlines just weeks after his study concluded, the media-savvy Zimbardo (who died in October) spent much of his career promoting the theory that putting good people in bad situations makes them do bad things. Abu Ghraib was, for obvious reasons, another big moment for him. When the acclaimed indie film The Stanford Prison Experiment hit theaters in 2015, starring Billy Crudup as Zimbardo and a pre- Succession Nicholas Braun as a subject, it joined a global canon of movies that reinforced his read on what happened in that Stanford hallway. The problem, as director Juliette Eisner demonstrates in her riveting Nat Geo documentary series The Stanford Prison Experiment: Unlocking the Truth , is that Zimbardo’s account of the study was far from definitive. The conclusions he drew about our moral malleability may be more pop psychology than science.

Many of the short docuseries that proliferate on streaming play like features chopped into episodes for viewers who’d rather binge on TV than commit to a whole movie. But the three-part Unlocking the Truth , which premieres Nov. 13 (and will stream the following day on Hulu and Disney+), functions as a true triptych. Through new interviews with participants and clips of the so-called “Stanford County Prison,” the first episode provides a chronology of the experiment that is largely faithful to Zimbardo’s version. The second, titled “The Unraveling,” introduces Thibault Le Texier, a French researcher who has worked to debunk the experiment, and intersperses his insights with more participant interviews that complicate or outright contradict Zimbardo’s account. Twenty minutes into the episode—at what is roughly the midpoint of the series—onscreen text informs us that the prison clips we’ve been watching aren’t footage from the study but reenactments shot on a soundstage by Eisner's team, as “only a fraction of the experiment was filmed in 1971.” The finale pairs one of Zimbardo’s last-ever interviews with scenes of the real participants visiting the soundstage, advising the actors who portray them on what really happened and talking amongst themselves about the experience and its legacy.

A long history of Stanford Prison Experiment dissent

Psychologists have been critiquing the Stanford Prison Experiment for as long as it’s been part of the discourse, though their points have mostly failed to penetrate the public consciousness. Erich Fromm picked apart Zimbardo’s methods in his 1973 book The Anatomy of Human Destructiveness , concluding that “ the difference between the mock prisoners and real prisoners is so great that it is virtually impossible to draw analogies from observation of the former.”

In 2002, the BBC aired a program called The Experiment , which documented British psychologists Alex Haslam and Steve Reicher’s restaging of the Stanford study . With an onsite ethical committee and the experimenters observing rather than participating (Zimbardo had acted as SCP’s superintendent), the prisoners wound up banding together and using their solidarity to extract better conditions. Haslam and Reicher have also noted that Zimbardo might’ve influenced guards’ behavior by making suggestions like this direct quote from a pre-experiment training session: “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… They can do nothing, say nothing, that we don't permit.” (There is, of course, the possibility that the presence of TV cameras affected the outcome of Haslam and Reicher's own experiment.)

Even the ad Zimbardo placed to recruit participants could have unwittingly influenced the behavior he observed. As Maria Konnikova described in a New Yorker essay that coincided with the 2015 film, psychologists Thomas Carnahan and Sam McFarland found , in 2007, that the presence of the words “prison life” in the ad likely narrowed the field of potential participants. When they ran their own experiment to see if they would receive different types of respondents by publishing the ad both as written and with the latter phrase omitted, Konnikova writes, they found that “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.”

How Unlocking the Truth furthers the case against the Stanford Prison Experiment

Le Texier, who published his findings in an American Psychologist article and the book Investigating the Stanford Prison Experiment: History of a Lie , identified additional problems with the study by scrutinizing Zimbardo’s archives. In the series, he explains that not only did the professor hold a “Day 0” orientation for guards in which he encouraged them to make prisoners feel powerless; he also distributed documents to them including a list of rules and suggested daily schedule. Along with making choices for the guards that they were represented as having made on their own, Zimbardo’s extensive instructions made it unclear whether the guards should’ve seen themselves as subjects of the experiment or as confederates in running it.

But Le Texier is far from Eisner’s only source who breaks with Zimbardo. Doug Korpi, a prisoner who was sent home after what has been portrayed as an emotional breakdown, says he was really just acting out of frustration after discovering how tough it would be to get dismissed from what he viewed as a bad job. A guard named John Mark recalls the warden, a grad student of Zimbardo’s, taking him aside for a “pep talk” urging Mark to be tougher on inmates. Dave Eshleman, the notorious guard nicknamed “John Wayne” (not a compliment among college students of the era), has said before that he was an actor and saw the experiment as a role. Here, he also notes that he and other subjects perceived Zimbardo’s goal of indicting the carceral system, supported that aim, and thus behaved in a way that reflected that “we would’ve done anything to prove this prison system was an evil institution.” (Now, as Eisner shows us, the theatrical Eshleman plays in a British Invasion tribute band.)

Most remarkable, to my mind, is Eisner’s interview with a man, identified in Le Texier’s research, named Kent Cotter. “I’m the guy that you never heard about, that you should be hearing about,” he says. (Indeed, googling “Kent Cotter” with “Stanford Prison Experiment” before Unlocking the Truth ’s premiere yielded zero English-language results.) “Because I am the guy that quit.” Assigned to be a guard, Cotter showed up to the training session but was alienated by Zimbardo’s agenda, as well as by his fellow guards’ gleeful plans for tormenting prisoners. “I felt more and more isolated from that group,” he recalls. So he quit before the experiment even started. “This was set up for the guards to abuse, so how could it go any other way?”

Why Zimbardo’s interpretation has persisted for so long

In his American Psychologist paper , Le Texier identifies four reasons why the Stanford Prison Experiment has remained so influential, despite conspicuous flaws. Two explanations have to do with ongoing debates around situationism —the idea that circumstances, more than personality, drive human behavior—within the field of psychology. Le Texier also concludes that:

"The SPE survived for almost 50 years because no researcher has been through its archives. This was, I must say, one of the most puzzling facts that I discovered during my investigation. The experiment had been criticized by major figures ... yet no psychologist seems to have wanted to know what exactly the archives contained. Is it a lack of curiosity? Is it an excessive respect for the tenured professor of a prestigious university? Is it due to possible access restrictions imposed by Zimbardo? Is it because archival analyses are a time-consuming and work-intensive activity? Is it due to the belief that no archives had been kept?"

Finally, Le Texier acknowledges the tireless promotional efforts of the experiment’s mastermind; “in his desire to popularize his experiment,” he writes, “Zimbardo has very often made the SPE look more spectacular than it was in reality.” That’s putting it mildly. Unlocking the Truth shows clip after clip of Zimbardo flogging his findings , decades after the experiment was conducted: MSNBC , The Daily Show , a panel with the Dalai Lama, a TED Talk , etc. He shored up his legacy as the media’s favorite social psychology expert with books like 2007’s The Lucifer Effect , a best seller and APA William James Book Award winner that highlights connections between the Stanford Prison Experiment and Abu Ghraib, and by hosting the 1990 PBS series Discovering Psychology . What’s the appeal of the message he’s pushing? From police brutality to genocide, “he has a very simple explanation to these very complex world events,” Le Texier says in the series.

It shouldn’t escape our notice, either, that Zimbardo was intimately involved with several previous onscreen representations of the experiment. He co-wrote and served as an executive producer of the 1992 documentary Quiet Rage: The Stanford Prison Experiment . And the 2015 movie everyone liked so much? It’s based on The Lucifer Effect , and Zimbardo consulted on it.

What, if anything, did the Stanford Prison Experiment really prove?

Critics of Zimbardo’s work have put forth various theories as to what his experiment actually means. When you’re aware of the influence he and his aides exerted over the guards, the Stanford Prison Experiment can start to look like an exercise in confirmation bias . The BBC study, whose participants knew their conduct would be observed by a huge TV audience, might suggest that we should demand more transparency from the carceral system and similar institutions. In Unlocking the Truth , Stephen Scott-Bottoms, Professor of Contemporary Theatre and Performance at Manchester University, speaks to the effect SPE has had on the public imagination when he calls it “the most influential piece of performance art of the 20th century.”

Particularly persuasive is an argument one of the BBC researchers makes in the series. “We began to realize that actually leadership was absolutely critical,” Reicher recalls. “Because the more you look at Zimbardo’s study, you realize that the guards didn’t become guards willy-nilly. He acted as leader to tell them what to do. But without leadership, you don’t get the types of toxic behavior we saw in Zimbardo’s SPE.” In other words: The situation to which Zimbardo attributed so much power is, in truth, only as powerful as the influence exerted by its leaders.

For me, the most crucial conclusion to draw from Unlocking the Truth and other research that has challenged the SPE is that people—some of them, at least— are capable of acting as individuals regardless of the situation. Even with Zimbardo’s encouragement, not every guard turned into a monster. Cotter didn’t even stick around long enough to don his uniform. And the ones who did abuse their power often had reasons for doing so besides the reservoir of evil Zimbardo felt sure was waiting within each impressionable human soul to be tapped. Contrary to the arguments he has made over the years (Zimbardo testified for the defense in the Abu Ghraib trial), maybe people should be held accountable for their behavior within institutional or otherwise hierarchical settings. As authoritarianism trends , it’s a takeaway worth remembering.

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The Stanford Prison Experiment

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

Cara Lustik is a fact-checker and copywriter.

• Participants
• Setting and Procedure

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

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

Purpose of the Stanford Prison Experiment

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

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

Participants in the Stanford Prison Experiment

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

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

Setting and Procedures

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

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

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

Results of the Stanford Prison Experiment

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

It was noted that:

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

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

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

Impact of the Zimbardo Prison Experiment

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

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

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

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

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

Criticisms of the Stanford Prison Experiment

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

Ethical Issues

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

Why was Zimbardo's experiment unethical?

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

Lack of Generalizability

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

Lack of Realism

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

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

Recent Criticisms

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

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

Among the issues described:

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

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

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

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

Stanford University. About the Stanford Prison Experiment .

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

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