PPsychology.com

Theories / People in groups

The Stanford prison experiment

In August 1971 twenty four young men were paid to spend two weeks in a mock prison in a Stanford basement. The study was called off after six days. What it actually shows has been argued over ever since.

Published November 4, 2026. 5 sources at the foot of the page.

What it says

The study is a demonstration, not a theory. Volunteers were assigned at random to be guards or prisoners in a simulated prison. The question was what the roles on their own would do to ordinary people.

Within days some guards were handing out petty punishments, counts in the middle of the night and small humiliations. Several prisoners were upset enough to be released early. Philip Zimbardo, who ran the study, was also playing the prison superintendent inside it.

The conclusion drawn at the time was that the situation swallowed the person: give an ordinary man a uniform and a role and the role takes over. That reading went into textbooks, into a film and into arguments about real prisons.

What the six days looked like

The sequence, as the published account and the study archives record it.

  1. The selection

    Seventy five men answered a newspaper advertisement, and twenty four were kept after interviews and questionnaires.

  2. The coin toss

    Guard or prisoner was assigned at random, which is what lets the study say anything about roles rather than about people.

  3. The briefing

    The guards were told what kind of atmosphere to create, a point the archives later made a great deal of.

  4. The first days

    Counts, numbers in place of names, push ups, and nights broken up by whoever was on duty.

  5. The end

    Christina Maslach, a researcher visiting the basement, objected to what she saw, and the study stopped on the sixth day.

Where it came from

Zimbardo ran the study at Stanford in August 1971 with Craig Haney and Curtis Banks, paid for by the Office of Naval Research. The first full account appeared in 1973, in a criminology journal rather than a psychology one.

It reached the public long before it was examined closely. Zimbardo's own book, The Lucifer Effect, came out in 2007 and tied the study to the abuses at Abu Ghraib, which is how most people met it.

What holds up, and what does not

The weakest part is the one most often skipped. Ali Banuazizi and Siamak Movahedi showed in 1975 that students told only how the study was set up could guess how the guards would behave. Those are demand characteristics: the people in a study work out what is wanted and give it. If the behavior is that easy to predict from the instructions, it may be an expectation acted out rather than anything hidden coming loose.

Thibault Le Texier went through the tapes and papers and published the result in 2019. The guards had been coached toward a hard line. The most famous breakdown was described years later by the man himself as put on. The write up also smoothed over how much the staff stepped in. There is no straight replication, and the study would not be approved today. The nearest attempt is the BBC prison study, run by Stephen Reicher and Alexander Haslam and published in 2006. It found close to the opposite: the prisoners organized together, and the guards held back from using their power.

What it does not mean

It does not show that a role turns anybody into anything. Twenty four young men who answered an advertisement for a prison study are not a sample of people in general. The briefing told the guards most of what the study then reported. The narrower lesson is the one that survives: what people are told to be, and what they think is wanted of them, shapes what they do.

Check yourself

Three questions on what is above. Each answer says why.

  1. What does it mean to say the study had demand characteristics?

    1. The guards were paid more than the prisoners were
    2. The people taking part could work out what behavior was wanted
    3. The study ran for longer than it was meant to
    Show the answer

    Answer: B. Banuazizi and Movahedi found in 1975 that students told only the setup could predict how the guards would act. The behavior may be the expectation, acted out.

  2. Pick the statement the 2019 archival work supports.

    1. The guards were coached toward a hard line
    2. The guards were given no instructions of any kind
    3. The study ran the full two weeks as planned
    Show the answer

    Answer: A. Le Texier's reading of the tapes and papers found the guards were pushed toward a tough line. The study was stopped on the sixth day of fourteen.

  3. The BBC prison study is the nearest thing to a repeat. What did it find?

    1. The same drift into cruelty, in half the time
    2. The prisoners organized together and the guards held back
    3. That the roles made no difference to anybody at all
    Show the answer

    Answer: B. Reicher and Haslam reported prisoner solidarity and reluctant guards, which is close to the opposite of the 1971 account.

Sources

  1. Haney, C., Banks, C., and Zimbardo, P. (1973). Interpersonal dynamics in a simulated prison. International Journal of Criminology and Penology, 1.
  2. Banuazizi, A., and Movahedi, S. (1975). Interpersonal dynamics in a simulated prison: A methodological analysis. American Psychologist, 30(2).
  3. Reicher, S. D., and Haslam, S. A. (2006). Rethinking the psychology of tyranny: The BBC prison study. British Journal of Social Psychology, 45(1).
  4. Zimbardo, P. G. (2007). The Lucifer Effect: Understanding How Good People Turn Evil. Random House.
  5. Le Texier, T. (2019). Debunking the Stanford Prison Experiment. American Psychologist, 74(7).

Practice it on Learn

Learn teaches this study in Studies that changed the field, the first unit of the Landmark studies track. The unit reads it beside the Bobo doll, Milgram and Robbers Cave experiments, each against its original paper.

Practice the Stanford prison experimentSee what Learn is

Every lesson is free. Plus is optional. For adults 18 and over.

More theories