The Stanford Prison Experiment

stanfordIn the summer of 1971, on the campus of one of the nation’s top universities and under the supervision of a faculty member, 11 students tortured 10 others over a six-day period, all in the interest of “science.”

The Experiment

Intended to last two weeks, according to the study’s author, Professor Phil Zimbardo, the original focus of the experiment was to see “how individuals adapt to being in a relatively powerless situation.”

The scenario chosen was a simulated prison, built in the basement of the psychology building on Stanford’s campus. Since the research was to involve people, it had to and was approved by the Stanford Human Subjects Committee. The study was set to begin on August 17, 1971.

The Students

Chosen from a pool of 70 male applicants (participants were paid $15 per day, or about $84 per day today), 21 finalists were randomly divided into two groups at the beginning of the experiment with 11 being assigned as guards and 10 as prisoners.

The Guards

Divided into three smaller groups that each worked daily eight-hour shifts, the guards were outfitted with uniforms and mirrored sunglasses. Professor Zimbardo remained active on the scene, playing the role of the prison’s superintendent. He and his staff encouraged the guards to be cruel, albeit without physical abuse:

We can create boredom . . . a sense of frustration . . . fear in them, to some degree. We can create a notion of the arbitrariness that governs their lives, which are totally controlled by us . . . They will have no freedom of action [and] . . . we’re going to take away their individuality in various ways . . . . this should create in them . . . a sense of powerlessness.

To make the experiment more “authentic,” Zimbardo enlisted the help of Carlo Prescott, an ex convict. Having spent 17 years in the infamous San Quentin, Prescott was able to provide Zimbardo with details of brutal prison practices when the study was being designed. Some of these practices were later reenacted by the guards during the experiment.

The Prisoners

Told in advance only that they would be “arrested,” the prisoners had a very different experience:

The suspect was picked up at his home, charged, warned of his legal rights, spread-eagled against the police car, searched, and handcuffed – often as surprised and curious neighbors looked on . . . . The suspect was . . . formally booked . . . fingerprinted . . . and taken to a holding cell where he was left blindfolded . . . .

Eventually the prisoners were taken to the make-shift prison on campus where:

Each was stripped, sprayed with a delousing preparation (a deodorant spray) and made to stand alone naked for a while in the cell yard. Then each . . . was given . . . a loose smock with an identifying number . . . . A chain and lock were placed around one ankle, and their hair was covered with a nylon stocking .. . to simulate having their hair shaved off . . . .

Day One

Professor Zimbardo was disappointed with how the experiment began:

After the end of the first day, I said, “There’s nothing here. Nothing’s happening.” The guards had this antiauthority mentality. They felt awkward in their uniforms. They didn’t get into the guard mentality . . . .

At least one of the guards, Dave Eshelman, was sensitive to Zimbardo’s disappointment, which was matched by his own ennui:

It was a bit of a bore, so I made the decision I would take on the persona of a very cruel prison guard.

Days Two – Six

Other guards were slower on the uptake, and at least one was chastised for not being tough enough. Zimbardo is quoted as saying: “The guards have to . . . be what we call a tough guard. The success of this experiment rides on [it]. . . .”

With this kind of mandate, things soon escalated. Despite the prohibition against physical abuse, the guards began torturing the prisoners, including spraying them with fire extinguishers and stepping on their backs while they did push ups.

Other torture included sleep deprivation, solitary confinement in a “janitor’s cupboard,” and “stripping them naked [and] putting bags over their heads.”

Some of the prisoners “reacted with such extreme emotions that they were removed from the study before the end of five days.”

Guard Eshelman, characterized as the most abusive guard, was allowed to run amok. As he said:

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 . . . .

According to Professor Zimbardo, he didn’t stop the abuse because he had gone native:

By the third day I was sleeping in my office. I had become the superintendent of the Stanford county jail. That was who I was: I’m not the researcher at all. . . .

The End

Luckily, cooler heads prevailed. A former graduate student and friend of Professor Zimbardo, Christina Maslach (they had just started dating) stopped by the experiment to check on him and was horrified with what she saw:

I thought, “Oh my God, what happened here?” I saw the prisoners being marched to go down to the men’s room. I was getting sick to my stomach, physically ill. . . . No one else was having the same problem.

Professor Zimbardo was shocked by her reaction:

I didn’t see what she saw. And I suddenly began to feel ashamed. This is when I realized I had been transformed by the prison study . . . . At that point I said, ‘You’re right. We’ve got to end the study.”


The American Psychological Association conducted an investigation in 1973 and determined that no ethical standards were violated in the conduct of the Stanford Prison Study. However, together with other research abuses like the Milgram Experiments of 1960s, it provided the impetus for health and psychiatry professionals, as well as Congress, to begin to regulate human subjects research. As a result, according to Professor Zimbardo, “No behavioral research that puts people in that kind of setting can ever be done again in America.”

If you liked this article, you might also enjoy our new popular podcast, The BrainFood Show (iTunes, Spotify, Google Play Music, Feed), as well as:

Bonus “Not Everyone’s a Psychopath” Fact

Two of the guards were “good” and refused to abuse the prisoners. According to Zimbardo, one of them, Geoff: “even stopped wearing his guard’s sunglasses and military shirt. He even told us later that he had thought about asking to become a prisoner because he hated to be part of a system that was grinding other people down so badly.”

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  • So what does this mean? That we’re innately evil creatures?

  • @Logan I think it’s moreso that we’re submissive creatures beholden to our surroundings. Instead of crying foul on inhuman coniditions we seemingly begin to convince ourselves that what we’re seeing is actually normal/acceptable.

  • You should also include other facts that are typically overlooked when giving such dramatic outcomes that the experiment supposedly *proved* such as;

    First, the issue of selection bias. Selection bias is where you choose your subjects in such a way that they are not truly representative of the general population. In this case, Zimbardo advertised to students to participate in an experiment about “prison life”. Clearly, a large segment of the general population would be repulsed by such a concept, and you’ve got to have questions about anyone attracted to that idea. Thus, all applicants to the Stanford Prison Experiment were preselected for comfort with the idea of “prison life”.

    Most of the Stanford guards did not exhibit any cruel or unusual behavior, often being friendly and doing favors for the prisoners. The most notorious guard, nicknamed John Wayne, explained that he was simply trying to emulate Strother Martin’s character from Cool Hand Luke. Other analysts have found it difficult to support Zimbardo’s conclusions, since the allegedly poisonous environment did not affect most participants, and the most notorious participant explained that his motivation came from a completely different source.

    Zimbardo himself was also criticized for actively participating in the experiment as one of the characters. He was the prison superintendent. Although he may have restrained himself from having any influence on the experiment, the fact that he put himself in the position of ultimate active authority over the guards’ behavior calls this into question. Many designers of such experiments would summarily throw out such a study based on this alone.

    Some researchers have also questioned why Zimbardo neglected the effect of individual personalities, instead generally attributing all behavior to the prison environment. How did John Wayne’s behavior as a guard compare to his behavior outside the experiment? Was he generally a friendly guy, or might he already have been a royal jerk? We don’t know, so there was insufficient data to conclude that his behavior was changed by the experiment.

    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.

    I have one other issue with Zimbardo’s results that I didn’t find anyone else raising, and it goes back to my 15-point checklist in Skeptoid #37, How to Spot Pseudoscience. Zimbardo has dedicated much of his career to the promotion of the idea that bad environments drive bad behavior. I tend to be cautious of claims coming from sources dedicated to promoting them. The scientific method starts with a null hypothesis, not with a preconceived notion to justify; and that process invariably produces data that do not support the conclusion, and theories tend to change over time as a result. By my analysis, Zimbardo appears to be cherrypicking his results to justify the same conclusion that he has been promoting throughout his career. This doesn’t make him wrong, it just gives me cause for skepticism.

    Finally, It’s worth mentioning that by today’s standards, the Stanford Prison Experiment was unethical and could never be performed in the United States. However, this point is not relevant to the validity of the results, and in any event, it was perfectly legal at the time.”

    but there’s also other sources. I just enjoy this podcast ^_^