What Is… the Stanford Prison Experiment

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In this series, I dig a little deeper into the meaning of psychology-related terms. This week, we’ll look at the Stanford prison experiment.

The Stanford prison experiment was a social psychology study carried out at Stanford University in 1971. Researchers randomly assigned Male student volunteers to be either “prisoners” or “guards” in a mock prison set up in a building on the university campus. The study excluded potential participants with criminal backgrounds or psychological/medical issues. The goal was to examine how people were affected by the perception of having power. Funding came from the U.S. Navy.

The Mock Prison

The participants received $15/day. The researchers informed them in advance that they could leave at any time. The “prisoners” were picked up at their homes, blindfolded, taken to the police station and “booked,” and then taken to the “prison,” charged with armed robbery. Upon arrival, they were stripped, deloused, and given prisoner uniforms marked with identification numbers.

Wooden batons were given to the “guards” as symbols of power. They also received mirrored sunglasses to make it harder for prisoners to read them. Both “guards” and “prisoners” were instructed to call the “prisoners” by their ID numbers rather than their names. The “prison” involved 3-man cells and a closet designated for “solitary confinement.”

The lead investigator, Philip Zimbardo, acted as the “superintendent” of the “prison”, and told the “guards” to exert control over the “prisoners” and strip away their individuality. A research assistant acted as “warden.” Parts of the study were filmed.

Things start to get ugly

By the second day, things started going downhill. Zimbardo described one “prisoner” who started to “act crazy, to scream, to curse, to go into a rage that seemed out of control.” He was released from the study.

Things just got worse, and Zimbardo estimated that about 1/3 of the “guards” became sadistic, with behaviours like:

  • the “guards” forced “prisoners” to use buckets in their cells rather than going to the toilet
  • “guards” forced some “prisoners” to sleep on concrete or to go naked
  • one “prisoner” said he was on a hunger strike, and the “guards” forced him to go into “solitary confinement”
  • certain “prisoners” were given basic privileges to further demoralize those who didn’t get the same privileges
  • “prisoners” were forced to do pushups while guards stepped on their backs

The study was planned to last 2 weeks, but it was stopped after 6 days when Zimbardo’s girlfriend, a psychology grad student, pointed out what a disaster it was. By that point, three “prisoners” had already been removed early from the study.

The aftermath

Zimbardo claimed that the study showed that the participants had internalized their roles and that behaviour was influenced by the situation rather than individual personality traits. He believed that deindividuation strategies like using “prisoner” numbers rather than names contributed to this.

As a consequence of this study, the American Psychological Association developed ethics guidelines requiring institutional ethics review board approval studies are conducted.

Ethically, this study is full of problems. Setting that aside, though, it’s disturbing how readily people will act abusively towards others. The element of deindividuation made me think of the Holocaust (although obviously on a much different scale) – it”s easier to dehumanize a number than a person.

The Attica Prison riot in New York State happened in the same year, and it makes me wonder how much the same elements that were observed in the Stanford experiment came into play in the guards’ treatment of prisoners leading up to the deadly Attica riot.

Zimbardo’s Stanford Prison Experiment official website contains his description of the events that occurred, and contains photos and some videos (along with quite a bit of advertising). The experiment was the subject of the 2015 film The Stanford Prison Experiment.

What are your thoughts on the dynamics that emerged in the Stanford study?


The Psychology Corner: Insights into psychology and psychological tests

The Psychology Corner has an overview of terms covered in the What Is… series, along with a collection of scientifically validated psychological tests.

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Ashley L. Peterson


Ashley is a former mental health nurse and pharmacist and the author of four books.

20 thoughts on “What Is… the Stanford Prison Experiment”

  1. I bet the outcome was pretty accurate as to how homo sapiens react to having power or being stripped of identity. I worked in Clinical Genetics for a part of my career, and it was around the time that a huge scandal broke in Utah. About the abuse and ethical versus non-ethical treatment of people in institutions. Not prisons, but mental health institutions. There was a ‘training school” in a small town in middle Utah where a lot of cognitively challenged and severely disabled were sent. Warehoused is a better term in light of what came about as a result of the scandal. People in that institution (and other mental health ‘hospitals’) were found to have been sexually abused, physically abused, emotionally and mentally abused. Some were forced to live in conditions that were so shocking that a whole new standard of care was put into active use following the discovery. The School almost had to close its doors and I know their funding was compromised, which might have made the problem a bit worse. It’s difficult to hire competent and caring health care workers in that kind of setting, even today. Sadly this attracts the sadists to the field in my opinion.

  2. It’s scary. Humans are terrifying. I look at the people around me sometimes and think, ya know, if I were trapped with these folks in a disaster which ones would panic, which would be violent, who would grab all the supplies, etc.

  3. People are capable of many things. History has many examples that the temptations of power and personal enrichment via power are hard to pass up. Could this be why Communism has not succeeded? Also, people in power tend to want to stay in power. They seem reluctant to relinquish it or lose it. Maybe we’re oversimplifying the argument. Maybe someone who knows more could weigh in.

    When were a supervisor for our last job, we sought additional education. The two fields that sound so much alike and are very, very different were Human Resource Management (HRM) and Human Resource Development (HRD). The differences seem pertinent to your point about the dehumanization of referring to people by a number instead of a name.

    In HRM, which was housed in the business college, people are “work units,” and the management of HRM is to get more productivity out of these work units. In HRD, which was housed in the college of education and human development, people are individuals, and the goal is to develop them as human beings.We chose HRD and humanization.

    Post-script: the entire HRD program was disbanded while we were enrolled. It wasn’t a money maker. All the faculty went to other colleges or were “retired.” The school of business thrives. While other factors may be at play, and just these facts oversimplify the matter, this seems not an unfair representation of capitalist priorities (we live in USA).

    We wrote a draft post (and never posted it) about the power of names.

    We had heard of the Stanford Prison experiment. It is cautionary. And people are also capable of compassion, tenderness, Love, connection, support. We like to know that we are capable of: beauty, terror, and everything else. We want to keep our values in the forefront so that we can act wisely some of the time. (heart emojis)

  4. Very interesting study. WOII inspired a lot of questions I think about power and abuse. Millgram did his experiments too. I’m glad people do look into this, to learn more and therefore maybe (very maybe) prevent something like that happening again or at least to bring awareness to those dire situations.
    My aunt used to say: ‘Homo homini lupus’ or ‘A man is a wolf to another man’. She is a smart woman.

  5. I had heard of this before, like Stanley Milgram’s slightly more famous experiment. They are scary, although I do wonder how much we can generalise from them, given that on some level the people involved probably assumed that it was a “safe” environment. Then again, maybe the state makes people think that certain negative behaviours and environments are “safe.”

    It is scary and I suppose it shows how people can insidiously abuse power even in situations where it clearly is necessary for one side to have power over the other. I mean, I’m in favour of rehabilitative treatment for prisoners, but I think there are going to be a small core of brutal sadists who are basically going to need locking up for long periods, but you wonder what would happen to the guards in that situation.

      1. Actually this reminds me of an amusing story my late grandfather told me. He was an army medical orderly in the failed British invasion of Norway early in World War II. He had some German prisoners in the sick bay and he was trying out his schoolboy German on them and got put on a charge by an officer for “fraternising with the enemy”! I guess it shows how much armies and prisons necessarily impose that lack of empathy.

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