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Debunking the Stanford Prison Experiment Thibault Le Texier University of Nice Author Note Thibault Le Texier is associate researcher at the University of Nice. This research has been funded by the Région Centre, Ciclic Fund. I am particularly indebted to Richard Griggs for detailed comments and suggestions. I would like to thank too the participants in the Stanford prison experiment who agreed to answer my questions, along with Alex Haslam and the two other reviewers who discussed this paper in detail, James Lyle Peterson, Daniel Hartwig of the Stanford Library Special Collections, and Lizette Royer Barton of the Center for the History of Psychology at the University of Akron. The archival material presented in this paper have been published in French in book form in April 2018, under the title Histoire d’un mensonge : enquête sur l’expérience de Stanford , Paris. La Découverte. Correspondence concerning this article should be addressed to Thibault Le Texier, letexier_t[at]yahoo.fr.
Abstract The Stanford prison experiment (SPE) is one of psychology’s most famous studies. It has been criticized on many grounds, and yet a majority of textbook authors have ignored these criticisms in their discussions of the SPE, thereby misleading both students and the general public about the study’s questionable scientific validity. Data collected from a thorough investigation of the SPE archives and interviews with fifteen of the participants in the experiment further question the study’s scientific merit. These data are not only supportive of previous criticisms of the SPE, such as the presence of demand characteristics, but provide new criticisms of the SPE based on heretofore unknown information. These new criticisms include the biased and incomplete collection of data, the extent to which the SPE drew on a prison experiment devised and conducted by students in one of Zimbardo’s classes three months earlier, the fact that the guards received precise instructions regarding the treatment of the prisoners, the fact that the guards were not told they were subjects, and the fact that participants were almost never completely immersed by the situation. Possible explanations of the inaccurate textbook portrayal and general misperception of the SPE’s scientific validity over the past five decades, in spite of its flaws and shortcomings, are discussed. Keywords : Stanford prison experiment, P. G. Zimbardo, epistemology
because “two thirds of the guards did not commit sadistic acts for personal ‘kicks,’ the experiment seems rather to show that one can not transform people so easily into sadists by providing them with the proper situation” (Fromm, 1973, p. 57-58). Banuazizi and Movahedi (1975) examined the possibility of demand characteristics operating in the SPE. They provided 150 college students with a description of the procedure used in the SPE, the advertisement used by Zimbardo to recruit volunteers for the SPE, a description of the rights and privileges the subjects agreed to waive in order to participate, and a description of the arrest and incarceration procedures in the SPE. Banuazizi and Movahedi used a set of open-ended questions to determine the students’ thoughts as to what the experimenter’s hypothesis was and their expectations regarding the outcome of the experiment. 81% percent of the tested students accurately figured out the experimenter’s hypothesis (that guards would be aggressive and that prisoners would revolt or comply), and 90% predicted that the guards would be “oppressive, hostile, aggressive, humiliating” (p. 158), thereby supporting the argument that demand characteristics were likely operating in the SPE and that the participants in the SPE would have probably guessed how Zimbardo and his co-experimenters wanted them to behave. Lovibond, Mithiran, and Adams (1979) extended the SPE by studying the effects of changes in the social organization of prison environments. Some aspects of the study replicated the SPE (e.g., volunteers were screened for possible psychological disorders), and some did not (e.g., the prisoners wore standard prison uniforms). 60 male volunteers were selected from a set of respondents to a newspaper advertisement. Three experimental prison regimes were examined. The Standard Custodial regime was modeled on existing medium- high security prisons; the more liberal Individualized Custodial regime allowed the prisoners some individuality and self-respect; and the Participatory regime encouraged the guards to engage in constructive and responsible behavior with the prisoners. The three regimes led to strikingly different guard-prisoner relationships. The Standard Custodial regime led to much hostility between the prisoners and guards, but the guard-prisoner relationships in the other
two regimes were rather benign and different from that observed in the SPE, supporting the argument that Zimbardo and his co-experimenters’ guidance and demand characteristics likely played a major role in the SPE’s outcome. In 2002, two British social psychologists, Alex Haslam and Stephen Reicher, conducted a prison experiment similar to the SPE in collaboration with the BBC (Haslam & Reicher, 2003; Reicher & Haslam, 2006). Filmed by the BBC and shown on television in 2002, this study was not an exact replication of the SPE, and neither Haslam nor Reicher took on a leadership role in the prison or provided guidance for the guards as Zimbardo had done in the SPE. The findings were also different from those in the SPE, again supporting the argument that Zimbardo’s guidance and demand characteristics likely played a major role in the outcome of the SPE. Reicher and Haslam concluded that “people do not automatically assume roles that are given to them in the manner suggested by the role account that is typically used to explain events in the SPE” (2006, p. 30). A few years later, based on a replication of the selection process of the SPE, Carnahan and McFarland argued that the participants in the SPE might have been self-selected. According to them, “men who choose to volunteer for a study advertised as a ‘psychological study of prison life’ may well be drawn to it because of a fit to their particular personalities. Indeed, it is hard for us to imagine otherwise, particularly so because the study is advertised as lasting more than a week and would likely place participants in an unusual and intense situation” (Carnahan & McFarland, 2007, p. 605). Other critiques have mainly been interpretations of the accounts of the SPE published by Zimbardo – accounts which were inaccurate and biased, as we shall see. These critiques emphasized in particular that Zimbardo, acting as prison superintendent, essentially indicated to the guards how to behave during his guard orientation (e.g., Bartels, 2015; Gray, 2013; Griggs, 2014; Haslam & Reicher, 2012; Krueger, 2008). Yet, they did not offer new data from which to evaluate the scientific validity of the SPE. The SPE has also been widely criticized for its unethical treatment of the participants
Archives of the History of American Psychology, University of Akron, Ohio (1 box). This entailed analyzing hundreds of paper documents, 6 hours of film recordings made during the experiment, and 48 hours of audio recordings made during, before and immediately after the experiment. Some of these documents have been digitized and made researchable in plain text, which facilitated this analysis. The findings from the archival content analyses were supplemented in two ways. First, semi-structured phone interviews were conducted between May 2017 and December 2017 with 15 participants in the SPE. Given the fact that the events took place 47 years ago, these interviews were mainly used to corroborate findings from the archival content analysis. Second, the archival content findings were compared with the textbooks, academic publications, and nonfiction books referring to the SPE, along with text searches on Google, Google Scholar, and Google Books for any additional discussions of the SPE. Results The description and discussion of the archival content analysis will be structured around seven main findings: (1) in designing the SPE, Zimbardo borrowed several key elements from a student experiment conducted 3 months before, (2) the guards knew what results Zimbardo wanted to achieve and how to achieve them, (3) the guards were asked to play a specific part but were not informed that they were subjects, (4) the prisoners could not leave of their own will and were subjected to harsh conditions designed by the experimenters, (5) the participants were almost never completely immersed in the unrealistic prison situation, (6) the collection and the reporting of the data were incomplete and biased, and (7) the conclusions of the SPE had been written in advance according to non-academic aims. I must add that a debate recently occurred online after the publication, in June 2018, of an article by journalist Ben Blum (Blum, 2018), which contained some findings taken from my book published a month and a half earlier in France (Le Texier, 2018). Zimbardo published a response to the main critiques raised by Blum on the official website of the SPE
(Zimbardo, 2018), but his response did not address most of the findings and arguments presented in my book and this paper, although he was aware of them: I sent him the first version of this paper on April 10, 2018. A detailed discussion of each of the seven main findings follows. The SPE was modeled after a student experiment: The Toyon Hall experiment According to Zimbardo’s accounts of the SPE, the experiment was born out of his former studies. For instance, Zimbardo told a Toronto Symposium in 1996: I had been conducting research for some years on deindividuation, vandalism and dehumanization that illustrated the ease with which ordinary people could be led to engage in anti-social acts by putting them in situations where they felt anonymous, or they could perceive of others in ways that made them less than human, as enemies or objects […] [I wondered] what would happen if we aggregated all of these processes, making some subjects feel deindividuated, others dehumanized within an anonymous environment in the same experimental setting, and where we could carefully document the process over time. (“The Stanford prison experiment: Still powerful after all these years,” Stanford Report , 1997, p. 8) The archives disclosed in fact that the SPE grew out of a student experiment that took place in a Stanford University dormitory in May 1971, under the direction of one of Zimbardo’s undergraduate students, David Jaffe (a fact noted in Haslam & Reicher, 2017, p. 133, but not investigated). Earlier in 1971, Zimbardo had proposed to the students in his seminar for undergraduates that they make presentations for half of the class meetings. Among the topics he proposed for them to consider were the impact of old age homes on their inmates, the street culture of the drug addict, people joining cults, and the effects of prisons on prisoners (Burton, 2016; Zimbardo, 2007a, p. 495 ). Jaffe and four other students picked the prison topic, and Jaffe took charge of the group. He read about prisons and visited a county jail in San Mateo; he met an ex-convict, Carlo Prescott; but he had difficulty motivating his group. A graduate student in psychology, Terry Osborne, suggested that he simulate a mock prison during a weekend, and when Jaffe proposed the idea to his group it was accepted, as Jaffe wrote a few weeks later in a report
the contributions to this research by David Jaffe who served as ‘warden’ and pre-tested some of the variables in the mock prison situation.” (Haney, Banks & Zimbardo, 1973, p. 97 ). An article published in 1999 briefly mentioned the Toyon Hall experiment (Zimbardo, Maslach & Haney, 1999, p. 204), and The Lucifer Effect , the book which Zimbardo devoted to the experiment 36 years later, speaks of it only in an end note where he acknowledges that the rules used in his experiment “were an extension of those that Jaffe and his comrades had developed for their project in my social psychology class” (Zimbardo, 2007a, p. 495), without specifying what this project was about. In 47 years, Zimbardo has given the Toyon Hall experiment some credit only once, in a lengthy biographical interview published in 2016 in digital form (Burton, 2016). Otherwise, David Jaffe is rarely credited as an instigator of the SPE, and he is hardly mentioned in articles and reports devoted to it. On the contrary, Zimbardo often presents him as “Warden David Jaffe, also an undergraduate student” (Zimbardo & White, 1972, p. 4), suggesting that he was one of the volunteers, and not one of the experimenters. Experimenters are of course entitled to replicate an experiment. Yet, when they do so, they have to explain which elements they drew from the previous experiment and which ones they chose to dismiss or modify, and why. Several key elements of the SPE have been presented as imagined by the guards (such as the rules and the daily schedule), when in fact these elements were directly drawn from the Toyon Hall experiment. The guards were trained Over the years, Zimbardo has maintained that the guards and the prisoners were left free and reacted spontaneously to the situation. In his first academic paper on the SPE, he stated, for instance, that “neither group received any specific training in these roles” (Haney, Banks & Zimbardo, 1973, p. 69 ). He asserts similarly in The Lucifer Effect that the “guards had no formal training in becoming guards, were told primarily to maintain law and order, not to allow prisoners to escape, and never to use physical force against the prisoners, and were
given a general orientation about the negative aspects of the psychology of imprisonment” (Zimbardo, 2007a, p. 56). According to the official accounts of the SPE, the guards invented on their own an impressive array of mistreatments: Upon arrival at our experimental prison, each prisoner was stripped, sprayed with a delousing preparation (a deodorant spray) and made to stand alone naked for a while in the cell yard. (Haney, Banks & Zimbardo, 1973, p. 76) Nakedness was a common punishment, as was placing prisoners’ heads in nylon stocking caps (to simulate shaved heads); chaining their legs; repeatedly waking them throughout the night for hour-long counts; and forcing them into humiliating “fun and games” activities. (Zimbardo, 2007b, p. B7) After 10 p.m. lockup, toilet privileges were denied, so prisoners who had to relieve themselves would have to urinate and defecate in buckets provided by guards. (Zimbardo, Banks, Haney & Jaffe, 1973, p. 39) After the rebellion on the second day, the guards… take the blankets off the prisoners’ beds in Cells 1 and 2, carry them outside the building, and drag them through the underbrush until the blankets are covered with stickers or burrs. Unless prisoners don’t mind being stuck by these sharp pins, they must spend an hour or more picking out each of them if they want to use their blankets. (Zimbardo, 2007a, p. 59) After the first day of the study, practically all prisoners’ rights (even such things as the time and conditions of sleeping and eating) came to be redefined by the guards as “privileges” which were to be earned for obedient behavior. (Haney, Banks & Zimbardo, 1973, p. 94) Push-ups soon become a staple in the guards’ control and punishment tactics. (Zimbardo, 2007a, p. 45) Far from encouraging this violence, Zimbardo is supposed to have prevented the guards from giving themselves completely over to it. He explained, for instance, during the trial of one of the Abu Ghraib guards, for which he served as expert witness: “I would typically intervene if a guard was being abusive…I was seen as the liberal administrator who was really protecting the prisoners” (Frederick, 2004, p. 574). The archival materials reveal that this narrative of guards becoming spontaneously violent is inaccurate, for at least five reasons. (1) The guards knew what results the experiment was supposed to produce. Zimbardo and his assistants announced the objectives of the experiment to the guards during their
degree. We can create a notion of the arbitrariness that governs their lives, which are totally controlled by us, by the system, by you, me, Jaffe. They’ll have no privacy at all, there will be constant surveillance – nothing they do will go unobserved. They will have no freedom of action. They will be able to do nothing and say nothing that we don’t permit. We’re going to take away their individuality in various ways. They’re going to be wearing uniforms, and at no time will anybody call them by name; they will have numbers and be called only by their numbers. In general, what all this should create in them is a sense of powerlessness. We have total power in the situation. They have none. (Musen & Musen, 1992, 5:07-5:44; Zimbardo, 2007a, p. 55) The experimenters also imposed programs on the guards’ behavior dependent upon the phase of the experiment and the time of day. For example, Jaffe informed them on the guard orientation day about the reception of the prisoners: “I have a list of what happens, some of the things that have to happen. When they get here, they’re blindfolded, they’re brought in, put in the cell or you can keep them out in the hall I imagine, they’re stripped, searched completely, anything that they have on them is removed” (Tape 2, 1971, transcription p. 5 ). Jaffe was reading a list handwritten by Zimbardo entitled: “Processing in – Dehumanizing experience,” which indicates for instance: “Ordered around. Arbitrariness. Guards never use name, only number. Never request, order.” (Outline for guard orientation, undated, p. 1) In addition to planning in detail the reception of prisoners, the experimenters also codified the course of action for the remaining days. Zimbardo distributed a “Suggested daily schedule” to the guards during the same orientation day (see Supplemental Material B). This program was directly copied from the Toyon Hall experiment, including the middle of the night counts, the work periods, and the “group therapy” sessions that never actually happened (Jaffe, 1971, p. 5). The schedule had been originally devised by Jaffe based on his research on prisons and it was usually followed, as Jaffe noticed in the notebook he kept daily: Aug. 17 “Schedule followed pretty carefully.” […] Aug. 18. “Daily schedule followed pretty closely” […] Aug. 19. “Again, basic schedule followed pretty closely” (Jaffe, undated a, p.3, p.4 and p.5) (3) During their orientation day, the guards received instructions from the experimenters. In several aspects, this orientation day was a training day. Jaffe gave the
guards specific recommendations drawn from his Toyon Hall experiment. For example, he told them that during the counting sessions they had to impose forced silence. What we did for the Count was: all lined up against the wall and then they had to count off, first of all “one, two three, four, five,” and they were in no mood to be cooperative so it took quite long time, then they had to call off their numbers, and again we didn’t have much count cooperation. And then they had to count off and call off their numbers. It took about 40 minutes, and then at the end of this the guard on duty had to repeat “Yes we all enjoyed the count, Mr. Correctional Officer” several times. What worked well at that time, a certain sarcasm sometimes that the guards used, “Ah, that’s too bad!”, that sort of thing, well you’ll each develop your own styles, these are conveyers but this was very effective and they hated the Count[.] […] Count is a good time for usually the guards use it to somewhat humiliate or be sarcastic[.] […] Right before the count we had the reading of the rules, we didn’t do it here, but that was another thing that was quite bothersome to the prisoners. The fact that they had to stand while the warden was there and listen to the rules being read. What we had, we had a lot of howling and chanting and all that sort of thing that went on and every time they [ garbled ] this might be something you might want to incorporate into daily routine. Then we had dinner after the count 5:30, then at 6:00 we had work that was shoe shining at that time. I had this blanket, [… and one day I took it out and] got it completely filled with straw and I thought to myself this would be a perfect work task to have them sit and pull out all the burr and the straw, cos I tried it one day and I didn’t make any headway at all. It takes hours, so if anybody has something like that, or maybe we can use one of the prisoners blankets. […] We woke them up at 6:00 in the morning, we had exercises for a while which consisted in walking around the cell block. You can add things to that. […] You could have them do jumping jacks, or push-ups or you know, you all know how to do basic health-stuff like that. (Tape 2, 1971, transcription p. 10-15) Several guards applied this program, including counting, taunting, reading the rules, chanting, push-ups, shoe shining and blanket cleaning. Guard Terry Barnett, for example, noted on the first day in his report: “activities of count – number recitation, several times, rule reading, intro. speech by Warden, push-up penalties for incompetence” (Barnett, 1971a). In an interview given in 2005, the ex-convict who served as a consultant before and during the SPE, Carlo Prescott, explained that “ideas such as bags being placed over the heads of prisoners, inmates being bound together with chains, and buckets being used in place of
experimenters asked the guards not to follow their instinctive reactions but to play a specific role. A guard, Mike Varn, reported for example at the end of the experiment that several times “the warden or Prof. Zimbardo specifically directed me (us) to act a certain way (ex. hard attitude Wednesday following Tuesday leniency).” (Varn, 1971, p. 1) Jaffe confessed, at the end of the experiment: I believed (and I still do) that without rules, without gruff and mildly realistic guard behavior, the simulation would have appeared more like a summer camp than a prison. […] Furthermore, even before I arrived, Dr. Zimbardo suggested that the most difficult problem would be to get the guards to behave like guards. I was asked to suggest tactics based on my previous experience as master sadist, and, when I arrived at Stanford [after a summer job in Chicago], I was given the responsibility of trying to elicit “tough-guard” behavior. (Jaffe, undated b, p. 1) Here for example is how Jaffe straightened out one of the soft guards on the third day: [T]he guards have to know that every guard is going to be what we call a tough guard. […] Because whether or not we can make this thing seem like a prison, which is the aim of the thing, depends largely on the guards’ behavior. […] And hopefully what will come out of this study is some very serious recommendations for reform. At least reform if not a revolutionary type of reform. And this is our goal. […] [S]o that we can get on the media and in the press with it, and say now look at what this is really about. […] [W]e need you to play the part of, you know, tough guard. […] [T]ry and react as you picture the pigs reacting. (Tape A, 1971, transcription, p. 8-11 and p. 13-16) Contacted by Ben Blum after the publication of my book, I sent him these extracts (e- mail, May 3, 2018), which he quoted in his article online (Blum, 2018). Two weeks later, in his statement on the official website of the SPE, Zimbardo recognized that “the research team asked all guards to be actively involved and firmly in control of the prisoners” (Zimbardo, 2018, p. 5). Yet he still maintained that the experimenters “did not give any formal or detailed instructions about how to be an effective guard” (Zimbardo, 2018, p.4). The evidence presented above directly contradicts this statement. (5) In order to get their full participation, Zimbardo intended to make the guards believe that they were his research assistants. On their orientation day, Zimbardo included the guards among the experimenters (“we can create boredom … we’re going to take away their
individuality … we have total power”), as noted by Haslam and Reicher (2003, p. 22). Zimbardo’s student Banks told them they were a “source of observation” (Tape 2, 1971, transcription p. 9 ). They had to complete daily reports and, if necessary, a “critical incident report sheet” (Critical incident report sheet, 1971). Together they formed a team of experimenters responsible for the maintenance of order and for the production of scientific results – as we will see in the next section, the two seem to have been inseparable from the guards’ point of view: the more they would get into their role as guards, the better the results. To reinforce their identification with the experimenters, Zimbardo made the guards believe that the experiment was only about the prisoners. He admitted it during a discussion with the guard John Loftus, a year after the experiment, who told him: [W]e knew we were being listened to by somebody but we didn’t know where or… There is one time when a guard said “Zimbardo is allowed to be testing us too,” and another guard said: “No, no, they told us we were supposed to keep these, you know…” It was our job to make sure this was a simulated prison, not that we were being experimentees too. […] We didn’t know until the end of the experiment that we were being experimented with. […] [W]e thought everything was under surveillance”. (Interviews re: Stanford Prison Experiment (Zimbardo, Korpi, John Loftus), 1972, side B, 26:50 and 30:35) Other guards expressed the same idea in the reports they wrote for Zimbardo, e.g.: [F]rom the beginning of the experiment, to the end, I thought of the guards as being a helping agent to the “experiment,” not actually part of it. I thought of the prisoners and their reactions etc. as being the experiment. I took care to make sure that I played a guard (as I thought a guard to be). I felt that any niceness on my part would eliminate me from the experiment. (Cerovina, undated, p. 1) Zimbardo admitted in The Lucifer Effect that he was interested in the “psychology of imprisonment,” not in the “psychology of maintaining law and order” (Zimbardo, 2007a, p. 55 and p. 208). But in no account, no article, or no book, does he specify that he deceived the guards and made them believe they were not subjects. Admittedly, the use of deception is not forbidden in psychological experiments, but it must be specified in the accounts of them, because it changes the interpretation that we can have of the participants’ reactions.
As we have seen, Banuazizi and Movahedi have shown that 150 college students who had been explained the SPE’s protocol could guess at 90% that the experimenters expected the guards to be “oppressive, hostile, aggressive, humiliating” (Banuazizi and Movahedi, 1975, p. 158). Zimbardo often ignores this criticism (for example, the term “demand characteristics” is not used in The Lucifer Effect ). On other occasions, Zimbardo invites his readers “to look to circumstances where role demands were minimal, where the subjects believed they were not being observed, or where they should not have been behaving under the constraints imposed by their roles,” (Haney, Banks & Zimbardo, 1973, p. 91 ). It is thus relevant, he often recommends, to concentrate on the night shift, and in particular the one officiated by David Eshleman, the toughest guard, nicknamed “John Wayne” by the prisoners. Yet, the guards seem to have felt they were being watched and filmed constantly (why should one do an experiment if it is not to observe its results?), and these abuses were especially related to one guard, Eshleman, who was a tall theater major, the son of a Stanford University professor, and who had just gone through a fraternity hazing (phone interviews, June 20, 2017 and November 11, 2017). Indeed, the abuses only concerned the first night shift, between 6pm and 2am; the team in charge of the second part of the night, from 2am to 10am, showed no particular inclination to sadism. Letters and recorded interviews kept in the archives reveal the strength of the demand characteristics. During the debriefing that took place on the last day of the experiment, Eshleman confessed for example to Jaffe: “I thought it would be better for the study if I presented what I thought to be a realistic relationship between guard and prisoner. […] [T]hroughout the entire experiment I was an actor, and I was hamming it up. […] I was role playing.” (Eshleman, 1971a, p. 2) Terry Barnett, the second most zealous guard, explained his involvement in the same terms. He wrote to Zimbardo, three months after the experiment: “I was always acting […] I was always very conscious of the responsibility involved in the guards’ and the experimenters’ positions; I mentioned this to various people at various times, including to you during the debriefing.” (Barnett, 1971b) He wrote to him again, three months
later: “I consciously felt that for the experiment to be at all useful ‘guards’ had to act something like guards. […] I felt that the experiment was important and my being ‘guard-like’ was part of finding out how people react to real oppression” (Barnett, 1972, p. 5). A reluctant guard, John Loftus, told Zimbardo a year after the SPE: “Most of the time I was conscious it was an experiment. It’s hard to remember now what I was thinking, but most of the time I was thinking: ‘I got to do this thing or else the experiment won’t come off right’.” (Interviews re: Stanford Prison Experiment (Zimbardo, Korpi, John Loftus), 1972, side B, 34:07) As Bartels noticed (2015, p. 47), the participants had also signed a contract with Stanford University, which stated: “[I understand that] I will be expected to participate for the full duration of the study, that I will only be released from participation for reasons of health deemed adequate by the medical advisers to the research project”. Bartels only quotes this part of the contract, but it also stipulated: “I will be expected to follow directions from staff members of the project or from other participants in the research project. I am submitting myself for participation in this research project with full knowledge and understanding of the nature of the research project and of what will be expected of me.” (Consent, 1971) Besides, the majority of the participants were in it for the money, as those I interviewed explained to me, and as Zimbardo admitted before a Congress subcommittee: “The pay was good ($15 a day) and their motivation was to make money.” (Zimbardo, 1971b, p. 154) But Zimbardo often adds that “since the subjects were all paid equally for their participation ($15 per day) and paid regardless of what actually occurred, there were no tangible incentives for them to behave in one specific way or another.” (Haney & Zimbardo, 1976, p. 268) In fact, the archival material discloses that the participants were paid at the end of the experiment, and thus that their pay depended on its duration and on their capacity to stay in it. This factor very probably reinforced the demand characteristics. Apart from the prisoners who asked to be released before the end of the experiment, most of the participants certainly wanted to keep this summer job as long as possible, and it could explain why no one ever intervened to bring it to an end. A reluctant guard, Geoff Loftus, who was asked two
