There is nothing to play here, deliberately — and the caution runs twice over.
Like Milgram, this is a procedure too harmful and too deceptive to reenact. But
the Stanford prison experiment needs a second warning:
the story almost everyone has heard about it did not survive the opening of its
own archives. What follows is both histories — August 1971, and what fifty years
of scrutiny left standing.
What is happening
In August 1971, twenty-one college-age men — judged
the most stable of some 75 volunteers who had answered a newspaper advertisement
offering $15 a day for a "psychological study of prison life" — were randomly
assigned to role-play prisoners and guards in a mock prison built in a Stanford
basement. Planned to run for up to two weeks, the study was stopped after six
days, by which point five prisoners had been released early, four with what the
report called extreme emotional depression, crying, rage and acute anxiety, and
one with a psychosomatic rash. The report itself calls the design exploratory: a
single treatment variable — which role a man was assigned — no specific
hypothesis, selectively dramatic recordings, and a small sample.Historical / descriptive
The authors read the week situationally: normal young men distorted by a
pathological situation, with personality tests predicting almost none of it. That
canonical story entered textbooks as proof of the power of roles; the modern
record complicates nearly every load-bearing part of it.
What this shows
Less than the textbooks claimed; more than nothing.
Whatever it failed to prove, the staged
prison was no theatre set. Conditions were genuinely punishing — prisoners were
woken at 2:30 a.m. and 6 a.m. for counts, wore ankle chains that bruised them,
and had toilet access restricted by day and replaced with buckets at night — and
the aftermath reshaped the discipline: the procedure has been treated as
ethically out of bounds ever since, field studies of this kind effectively
ceased, and for decades the only follow-up was a partial Australian
variation.Historical / descriptive
The second exhibit is stranger: the opened archives show, in unusual detail, how
a scientific parable gets made — and how far a clean moral can outrun its
evidence.
What this does not show
The study does not show that ordinary people,
handed a uniform and a role, reliably become cruel. That conclusion was contested
from the beginning and is now rejected by a substantial part of the field, which
reads the guards' behaviour as engaged followership of the experimenters'
leadership rather than natural role conformity — yet the canonical version kept
circulating: a 2014 analysis of thirteen introductory psychology textbooks found
eleven still presenting the study and only six mentioning any criticism of
it.Mixed / contested
A 1975 critique argued that the guards'
behaviour may reflect what participants understood the experimenters wanted
rather than any natural pull of the roles. When 150 students were given a
description of the study's procedure, 81% correctly guessed the experimental
hypothesis, and 90% predicted that the guards would be "oppressive, hostile,
aggressive, humiliating".Supported, with limits None of this proves the reverse — it shows these
guards were led, not that people never turn cruel unled. It simply cannot support
the claim made in the study's name: that the uniform alone does the work.
Research and limitations
The most consequential research on this study is research about it.
The guards were not left to invent their
behaviour. Archival research shows that staff briefed them on the atmosphere of
fear, arbitrariness and powerlessness the prison was meant to create; that the
"warden" — an undergraduate who had run a mock-prison class exercise three months
earlier, from which eleven of the seventeen prisoner rules were copied — pressed
reluctant guards to be a "tough guard"; and that several guards later described
their cruelty as performance for the experimenters. Zimbardo's reply conceded
that the team asked guards to be actively involved and firmly in control, while
insisting the pressure was mild and no brutality was instructed.Supported, with limits
Even the study's most famous moment is
contested testimony. The first prisoner released — whose screaming breakdown on
the second day anchors the canonical story — was recorded, on the day the study
ended, explaining that after learning he could not simply walk out he chose to
"just act mad"; he repeated that account for decades. Zimbardo maintained the
breakdown was genuine — the same man also called the study a deeply upsetting
experience — and archival work suggests that of the eleven men who passed through
the prisoner role, no more than two showed symptoms of a real nervous
breakdown.Mixed / contested
When the setup was revisited — the 2002 BBC Prison
Study, in which fifteen men lived as prisoners and guards for eight days under
independent ethical oversight, with no experimenter playing warden and no
coaching — the roles did not take over: the guards failed to identify with their
role and were reluctant to impose their authority, the prisoners eventually
overcame them, and the researchers concluded that people "do not automatically
assume roles that are given to them". It was a conceptual challenge rather than
an exact replication — and it ended, notably, in a drift toward a tyranny of the
participants' own making.Supported, with limits
Zimbardo consistently rejected the fraud framing, conceding chiefly that the
study lacked an independent scientific observer; his defence is cited here and
worth reading beside its critics. The original cannot ethically be rerun, so
this entry grades the study as history and contested interpretation, not as
evidence about human nature.
Research drawer — claims, sources and limits
Every highlighted claim above is recorded here with its evidence grade and sources. Grades are per claim; this site never computes an overall truth score.
↩ In August 1971, twenty-one college-age men — judged the most stable of some 75 volunteers who had answered a newspaper advertisement offering $15 a day for a "psychological study of prison life" — were randomly assigned to role-play prisoners and guards in a mock prison built in a Stanford basement. Planned to run for up to two weeks, the study was stopped after six days, by which point five prisoners had been released early, four with what the report called extreme emotional depression, crying, rage and acute anxiety, and one with a psychosomatic rash. The report itself calls the design exploratory: a single treatment variable — which role a man was assigned — no specific hypothesis, selectively dramatic recordings, and a small sample.
Haney, C., Banks, C., & Zimbardo, P. (1973). Interpersonal dynamics in a simulated prison. International Journal of Criminology and Penology, 1, 69-97. http://pdf.prisonexp.org/ijcp1973.pdf · accessed 2026-08-24 Support note: Reports the selection (21 participants from an initial pool of 75 respondents to an ad for a psychological study of 'prison life' at $15 per day; the 24 judged most stable were selected, randomly assigned, and data analysis rests on 10 prisoners and 11 guards), the contract 'for $15.00 per day for up to two weeks', the premature termination 'after only six days', and the five early releases: four with 'extreme emotional depression, crying, rage and acute anxiety' beginning as early as the second day, the fifth after a psychosomatic rash. Its own methodological caveats: 'no specific hypotheses were advanced other than the general one', a 'single treatment variable' design, recordings 'focussed upon the more interesting, dramatic events', incomplete data on all subjects, and 'a relatively small sample on which to make cross-tabulations'.
↩ The guards were not left to invent their behaviour. Archival research shows that staff briefed them on the atmosphere of fear, arbitrariness and powerlessness the prison was meant to create; that the "warden" — an undergraduate who had run a mock-prison class exercise three months earlier, from which eleven of the seventeen prisoner rules were copied — pressed reluctant guards to be a "tough guard"; and that several guards later described their cruelty as performance for the experimenters. Zimbardo's reply conceded that the team asked guards to be actively involved and firmly in control, while insisting the pressure was mild and no brutality was instructed.
Le Texier, T. (2019). Debunking the Stanford Prison Experiment. American Psychologist, 74(7), 823-839. https://doi.org/10.1037/amp0000401 · accessed 2026-08-24 Support note: From the Stanford and Akron archives plus interviews with 15 participants: Zimbardo's taped guard-orientation talk announced the boredom, fear, arbitrariness, lost privacy and 'sense of powerlessness' the prison should create; the undergraduate 'warden' had directed the Toyon Hall mock-prison class exercise in May 1971, three months before the SPE, 11 of the SPE's 17 prisoner rules were copied directly from it, and he wrote that he 'was given the responsibility of trying to elicit tough-guard behavior'; a taped talk records him telling a reluctant guard that 'every guard is going to be what we call a tough guard'; guards' letters and debriefings describe their cruelty as acting for the experimenters ('I was an actor, and I was hamming it up'; 'I was always acting').
Zimbardo, P. G. (2018, June). Philip Zimbardo's response to recent criticisms of the Stanford Prison Experiment. Stanford Prison Experiment official website (prisonexp.org). https://www.prisonexp.org/response · accessed 2026-08-24 Support note: Zimbardo's reply acknowledges that the warden told an inactive guard to be firm and involved in the action, and that the team wanted guards engaged, but argues the pressure was mild compared with real wardens, that physical force was explicitly banned, and that cruelty was never instructed — the guards who behaved cruelly, he maintains, did so on their own initiative while others remained 'good guards'.
↩ Even the study's most famous moment is contested testimony. The first prisoner released — whose screaming breakdown on the second day anchors the canonical story — was recorded, on the day the study ended, explaining that after learning he could not simply walk out he chose to "just act mad"; he repeated that account for decades. Zimbardo maintained the breakdown was genuine — the same man also called the study a deeply upsetting experience — and archival work suggests that of the eleven men who passed through the prisoner role, no more than two showed symptoms of a real nervous breakdown.
Le Texier, T. (2019). Debunking the Stanford Prison Experiment. American Psychologist, 74(7), 823-839. https://doi.org/10.1037/amp0000401 · accessed 2026-08-24 Support note: Quotes the archival tape made the day the study was stopped, in which the released prisoner says he 'made up several schemes whereby I could get out', choosing to 'just act mad, or upset'; documents that he maintained this account a year later, in the late 1980s and in recent interviews; summarizes Zimbardo's 2018 counterarguments (researchers must treat a breakdown as real, and the participant elsewhere called the study his most upsetting experience); notes the prisoners had learned they could not simply leave; and states that out of the 11 prisoners 'it looks like only two really exhibited symptoms of a nervous breakdown'.
Blum, B. (2018, June 7). The Lifespan of a Lie. Medium (GEN, 'Trust Issues' series). https://medium.com/s/trustissues/the-lifespan-of-a-lie-d869212b1f62 · accessed 2026-08-24 Support note: The June 2018 magazine article that made the acting account public. Only the freely readable opening could be accessed for this entry (the story is member-locked): it recounts the canonical breakdown scene of the evening of August 16, 1971. The Korpi and guard interview quotations it contains are known here second-hand, via Le Texier (2019) and Zimbardo's reply, and were not read directly.
↩ A 1975 critique argued that the guards' behaviour may reflect what participants understood the experimenters wanted rather than any natural pull of the roles. When 150 students were given a description of the study's procedure, 81% correctly guessed the experimental hypothesis, and 90% predicted that the guards would be "oppressive, hostile, aggressive, humiliating".
Banuazizi, A., & Movahedi, S. (1975). Interpersonal dynamics in a simulated prison: A methodological analysis. American Psychologist, 30(2), 152-160. https://doi.org/10.1037/h0076835 · accessed 2026-08-24 Support note: The peer-reviewed methodological critique of the SPE. The official abstract states that it questions the experimenters' key assumptions and final causal inferences on methodological grounds, offers empirical evidence to elucidate the criticisms, and develops an alternative, role-expectation interpretation. Full text paywalled; abstract read via the ERIC record (EJ115205).
Le Texier, T. (2019). Debunking the Stanford Prison Experiment. American Psychologist, 74(7), 823-839. https://doi.org/10.1037/amp0000401 · accessed 2026-08-24 Support note: Reports the survey figures from Banuazizi and Movahedi (1975, p. 158): 150 college students were given a description of the SPE procedure, recruitment ad, rights waiver and arrest arrangements; 81% accurately identified the experimenters' hypothesis and 90% predicted the guards would be 'oppressive, hostile, aggressive, humiliating'.
↩ Whatever it failed to prove, the staged prison was no theatre set. Conditions were genuinely punishing — prisoners were woken at 2:30 a.m. and 6 a.m. for counts, wore ankle chains that bruised them, and had toilet access restricted by day and replaced with buckets at night — and the aftermath reshaped the discipline: the procedure has been treated as ethically out of bounds ever since, field studies of this kind effectively ceased, and for decades the only follow-up was a partial Australian variation.
Le Texier, T. (2019). Debunking the Stanford Prison Experiment. American Psychologist, 74(7), 823-839. https://doi.org/10.1037/amp0000401 · accessed 2026-08-24 Support note: Documents from the archives that prisoners were awakened at 2:30 a.m. and 6 a.m., permanently wore ankle chains that caused bruises and disturbed sleep, were never allowed to shower, and had toilet access restricted during the day and forbidden at night, with buckets in the cells — harsh conditions arranged by the experimenters, cited by Le Texier from Zimbardo's own accounts and the archive.
Reicher, S., & Haslam, S. A. (2006). Rethinking the psychology of tyranny: The BBC prison study. British Journal of Social Psychology, 45(1), 1-40. https://doi.org/10.1348/014466605X48998 · accessed 2026-08-24 Support note: States that ethical concerns have placed the SPE 'off-limits' (with the exception of the partial replication by Lovibond, Mithiran and Adams, 1979, an Australian three-regime study), and that the SPE marked at once the culmination of post-war field studies and their cessation, contributing to the shift toward minimal-interaction laboratory paradigms.
↩ When the setup was revisited — the 2002 BBC Prison Study, in which fifteen men lived as prisoners and guards for eight days under independent ethical oversight, with no experimenter playing warden and no coaching — the roles did not take over: the guards failed to identify with their role and were reluctant to impose their authority, the prisoners eventually overcame them, and the researchers concluded that people "do not automatically assume roles that are given to them". It was a conceptual challenge rather than an exact replication — and it ended, notably, in a drift toward a tyranny of the participants' own making.
Reicher, S., & Haslam, S. A. (2006). Rethinking the psychology of tyranny: The BBC prison study. British Journal of Social Psychology, 45(1), 1-40. https://doi.org/10.1348/014466605X48998 · accessed 2026-08-24 Support note: The full report: 15 men studied over 8 days in a purpose-built institution, monitored throughout by two independent clinical psychologists and a five-person ethics committee; guards were told to make the institution run smoothly but were 'given no guidance about how they should achieve their goals'. Unlike the prisoners, the guards failed to identify with their role, were reluctant to impose authority, and were eventually overcome by a prisoner breakout on Day 6; the claim's quotation appears verbatim ('people do not automatically assume roles that are given to them in the manner suggested by the role account'). The authors state the aim 'was not to conduct an exact replication of the SPE', and report that by the end participants were close to instituting 'a new and more tyrannical social system' before the study ended at noon on Day 8.
↩ The study does not show that ordinary people, handed a uniform and a role, reliably become cruel. That conclusion was contested from the beginning and is now rejected by a substantial part of the field, which reads the guards' behaviour as engaged followership of the experimenters' leadership rather than natural role conformity — yet the canonical version kept circulating: a 2014 analysis of thirteen introductory psychology textbooks found eleven still presenting the study and only six mentioning any criticism of it.
Haslam, S. A., & Reicher, S. D. (2012). Contesting the "nature" of conformity: What Milgram and Zimbardo's studies really show. PLoS Biology, 10(11), e1001426. https://doi.org/10.1371/journal.pbio.1001426 · accessed 2026-08-15 Support note: Argues, for Zimbardo's study alongside Milgram's, that participants' cruelty reflected identification with the experimenters' cause and the leadership they provided (including Zimbardo's guard briefing) rather than a natural, automatic slide into role, and that the conformity reading of both studies is not supported by the evidence.
Griggs, R. A. (2014). Coverage of the Stanford Prison Experiment in introductory psychology textbooks. Teaching of Psychology, 41(3), 195-203. https://doi.org/10.1177/0098628314537968 · accessed 2026-08-24 Support note: The official abstract reports that of 13 contemporary introductory psychology textbooks analyzed, 11 discussed the SPE but only 6 even mentioned any of the criticisms, despite myriad published criticisms of both the situationist explanation and the methodology (including strong demand characteristics).