The Stanford Prison Experiment

What it is

The study was run by Zimbardo with Craig Haney and Curtis Banks as co-investigators. Volunteers were sorted into guards and prisoners, and Zimbardo took the role of superintendent of the prison. Its reputation outran its publication record. Robert Sapolsky reports that it has been cited more than 58,000 times, against more than 27,000 for Milgram's obedience studies and more than 4,000 for Asch's conformity work, and he notes that Zimbardo published remarkably little of the data in professional journals and mostly wrote for the lay public (Behave, pp. 464, 466-467).

Three claims travel under the name, and they should be separated. The first is that situations shape behaviour. The second is that a role alone is enough to make some people cruel. The third is that ordinary people given power become tormentors. The Stanford Prison Experiment is usually cited for the second and third.

In effect

The first claim holds, and it holds without Stanford. Sapolsky puts what is left of it this way: "a far higher percentage of perfectly normal people than most would predict succumb and do awful things," although "there are always those who resist" (Behave, pp. 468-469).

On the second claim, the archive now allows the experiment to be checked. Thibault Le Texier, working from the Stanford archive and interviews with 15 participants, reports that at the guard orientation Zimbardo described the aim of producing boredom, frustration and powerlessness and said, "We have total power in the situation. They have none." The orientation also covered counting routines and humiliation tactics, and the guards were not told they were research subjects (Le Texier, 2019). Participants' own accounts include a guard writing "I was always acting" and a prisoner writing that "the one thing that kept me there was the money." Only two of the 11 prisoners showed clear signs of breakdown.

Alexander Haslam, Stephen Reicher and Jay Van Bavel reach a compatible conclusion from the tapes by a different route. They argue that cruelty becomes likelier when leaders persuade people that their actions serve a noble cause, and read the guards' toughness as a response to leadership from the research team, a pattern they call identity leadership (2019). Sapolsky had made the experimenter point earlier from the design alone: Zimbardo acted as superintendent, told guards they could make prisoners feel afraid and helpless, and was, in Sapolsky's words, "someone whom you'd very much wish to please."

On the third claim, Thomas Carnahan and Sam McFarland recruited students with an advertisement close to the original and compared them with volunteers for a generic psychology study. Volunteers for the prison-life study scored higher on aggressiveness, authoritarianism, Machiavellianism, narcissism and social dominance and lower on empathy and altruism. The authors call the implications for the 1971 study speculative (2007). Sapolsky adds that if prisoners shared that makeup too, it is unclear why it would tilt the result toward brutality.

The nearest thing to a replication is the BBC Prison Study. Its guards did not adopt tyrannical roles. Reicher and Haslam read the outcome as identification and the failure of groups making tyranny seem acceptable. Sapolsky reads the same study as pointing to bad apples rather than bad barrels. Both readings are in the literature, and neither restores the 1971 claim.

What it does not say

It does not show that a role alone makes ordinary people cruel. It does not show that the guards' behaviour was spontaneous, since the archive records instructions. It does not settle whether leadership or disposition explains the BBC Prison Study.

It also does not rest on a single critic. On 28 August 2018 Zimbardo and Craig Haney, who conducted the Stanford study, joined Alexander Haslam and Stephen Reicher in a statement saying that the new information suggests traditional accounts understate how much the experimenters intervened, that their leadership helped drive the guards' brutality, and that people may not slip into roles as easily as once thought. The statement asks for open and respectful debate that stays with ideas. Zimbardo and Haney answered the 2019 papers in a 2020 comment listed on Zimbardo's site. The comment was not opened for this page, so their reply is part of the record but is not summarised here.

Cited accurately, the study is a case of what happens when people with scientific authority ask student guards for toughness. It is not a measurement of what roles do.

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