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Fifty Years of The Stanford Prison Experiment

Updated: Aug 23

Perhaps this infamous study has escaped due criticism in its time.

Phillip Zimbardo entertains students at a London Conference.

The Stanford Prison Experiment (SPE) is now fifty years old. It reached its fiftieth birthday on 15 August 2021, having become one of the most famous and notorious of all psychology studies. Although the research paper was published by Haney, Zimbardo and Banks, it is Phillip Zimbardo who is most closely associated with the SPE. The picture of Phillip Zimbardo (above) was taken at a London Psychology Conference in 2017 when he entertained the audience by dancing to Santana: now in his eighties, Zimbardo's energy could hardly be faulted.

The fame of the Prison Study though reveals a certain paradox: its status as a 'classic study' serves as a reminder of what mainstream psychology is not. Ethically problematic, scientifically dubious, biased and sensational, the Stanford Prison Experiment is as controversial as it is entertaining. Most A Level teachers of Psychology will know that talking about the study is a guaranteed way to boost Psychology A Level numbers. At the same time, one of the first messages to get across to Psychology students is that mainstream Psychology for the most part is simply not like the SPE.

Which brings me to the official procedure: in 1971, sixteen participants, randomly assigned to the role of guard or prisoner, took part in the day to day running of a mock prison in the basement of Stanford University. The guards were told to manage the prison, whilst the prisoners followed the guards' instructions, all monitored by researchers and video cameras. Power disparities were established from the start: the guards wore uniforms with sunglasses, and the prisoners wore long ‘dresses’ and stockings on their head. What happened was that after six days the study was halted following, amongst other events, a prisoner having a nervous breakdown, and guards becoming overly tyrannical in their punishment regime.

Haney et al. (1973) concluded that the evil situation of the prison prompted otherwise decent people to behave aggressively. According to Haney et al., ‘evil acts’ are ‘attributable to the operation of powerful social forces’ (Haney et al, 1973, p.35). In other words, when atrocities are committed in real situations, it is not the fault, or indeed the responsibility, of the individuals who commit them, but the ‘social forces’ that compelled them to do it. In such tyrannical environments, people conform to the social role given to them, just as the guards and prisoners conformed to their assigned role. Human beings are vulnerable to social variables to the extent where (logically) they cannot be held accountable for what they do. On the strength of this conclusion, Zimbardo later offered a defence for prison guards who had abused Iraqi prisoners in the Abu Ghraib scandal. The much publicised photographs of US military personnel torturing Iraqi detainees were – according to Zimbardo – the inevitable outcome of placing otherwise dutiful army reservists into the role of prison guard in the very prison where Saddam’s regime once executed dissenters. Thus the situation, not the individual perpetrators, is to blame.


The ethical problems related to the Stanford Prison Experiment have ironically protected it from further criticism. The very assertions that Haney et al. made in conclusion take backstage as the ethical breaches dominate attention. That is until more recently: in a 2019 paper, 'Debunking The Stanford Prison Experiment', Thibault Le Texier presents a damning case against the validity of Haney et al's methods and conclusions. For instance, Le Texier believes that the guards were coached into committing abuse against the prisoners, and were not acting particularly naturally when they were in the study. Indeed, following telephone interviews with the original participants, Le Texier suggests that behaviour was quite closely directed by the researchers. Moreover, the basement setting did not reflect the experience of being in a prison (which was confirmed by the participants) and, most revealing, the study had already been undertaken by some of Zimbardo’s students. During The Toyon Hall Experiment, conducted in 1971, prisoners came to accept the authority of the guards in little cited study (Le Texier, 2019, p.4).

Aside from issues of validity, the Stanford Prison Experiment offered a conclusion considered by some to be over simplistic. As Reicher and Haslam (2006) point out, not every guard did conform to the evil machinations expected of them: the guards showed as much dissent as they did conformity. This point is also echoed in the Abu Ghraib Prison where some American guards resisted abusing prisoners, which might suggest that ‘evil’ is a more dispositional factor than Haney et al thought.

In their 2006 BBC Prison Study, Reicher and Haslam took an arguably more nuanced view of group behaviour by explaining group dynamics through the work of Henri Tajfel. Although groups do act in oppressive ways, groups can also provide the foundation for progressive change. Group identity is subject to change if there is perceived insecurity and permeability. In the BBC Prison Study, like the Stanford Study, prisoners initially rebelled; however, unlike Stanford, the BBC prisoners first helped to establish a commune and, when this failed, a new tyranny emerged before the study ended early. It seems that tyrannical situations do not necessarily lead to social role conformity. It rather depends on how individuals categorise or appraise their group identity.

Reicher and Haslam's research can be found on this BBC link: http://www.bbcprisonstudy.org/

Despite the drawbacks of the Stanford Prison Experiment, there is concern that Psychology textbooks do not do enough to present them. Griggs (2014) sampled thirteen introductory textbooks for Psychology and noted that, of the eleven that covered the SPE, only six offered (rather meagre) criticism. Meanwhile five textbooks presented no criticisms at all. Whether textbooks writers do not have enough space for criticism or they are not aware of them is unclear. The effect is that students see the SPE as the gold standard psychology study and accept the conclusions at face value.

Stephen Reicher 'celebrated' the fiftieth anniversary of the Stanford Prison Experiment on Twitter with an extended thread about the limitations of the study. Stephen Reicher reminds us here that accepting the SPE conclusions is tantamount to letting preparators of abuse off the hook. He also reiterates the point that not all of the guards did conform to the tyrannical type that was being encouraged. If students read about the Stanford Prison Experiment in textbooks, and think that Haney et al.'s work had few weaknesses or contradictions, then is perhaps says something about the students and their sources of information. All scientific research is, and should be, subject to scrutiny. Perhaps the SPE's longevity lies in the fact that its conclusions are easily summarised, and textbooks would do well to reflect the newer, more nuanced research on group behaviour.


Haney, C., Banks, C. and Zimbardo, P. (1973) Interpersonal Dynamics in a Simulated Prison Study, Stanford University

Griggs, R. A., 'Coverage of the Stanford Prison Experiment in Introductory Psychology Textbooks', in Teaching of Psychology, 2014 41: 195, DOI: 10.1177/0098628314537968

Reicher, S. and Haslam, S. A. (2006) 'Rethinking the psychology of tyranny: The BBC prison study', The British Journal of Social Psychology Volume 45, Issue 1


LeTexier, T. (2019) 'Debunking the Stanford Prison Experiment', American Psychologist, 74(7), 823–839. https://doi.org/10.1037/amp0000401

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