Stanford prison experiment

This article is about the psychology experiment. For the American punk band, see Stanford Prison Experiment (band). For the 2015 film, see The Stanford Prison Experiment (film).
Plaque Dedicated to the Location of the Stanford Prison Experiment

The Stanford Prison Experiment (SPE) was a landmark study of the psychological effects of perceived power. Specifically, the study focused on the power struggle between prisoners and prison guards. The experiment was conducted at Stanford University on August 14–20, 1971, by a team of researchers led by psychology professor Philip Zimbardo using college students.[1] It was funded by the U.S. Office of Naval Research[2] and was of interest to both the U.S. Navy and Marine Corps as an investigation into the causes of conflict between military guards and prisoners. The experiment is a classic study on the psychology of imprisonment[3] and is a topic covered in most introductory psychology textbooks.[4]

The participants adapted to their roles well beyond Zimbardo's expectations, as the guards enforced authoritarian measures and ultimately subjected some of the prisoners to psychological torture. Many of the prisoners passively accepted psychological abuse and, at the request of the guards, readily harassed other prisoners who attempted to prevent it. The experiment even affected Zimbardo himself, who, in his role as the superintendent, permitted the abuse to continue.[5][6] Two of the prisoners quit the experiment early, and the entire experiment was abruptly stopped after only six days, to an extent because of the objections of graduate student Christina Maslach, whom Zimbardo was dating (and later married). Certain portions of the experiment were filmed, and excerpts of footage are publicly available.

Goals and methods

Zimbardo and his team aimed to test the hypothesis that the inherent personality traits of prisoners and guards are the chief cause of abusive behavior in prison. Participants were recruited and told they would participate in a two-week prison simulation. The team selected the 24 males whom they deemed to be the most psychologically stable and healthy.[7] These participants were predominantly white[8] and of the middle class.[9] The group was intentionally selected to exclude those with criminal backgrounds, psychological impairments, or medical problems. They all agreed to participate in a 7- to 14-day period and received $20 per day.

The experiment was conducted in the basement of Jordan Hall (Stanford's psychology building). 12 of the 24 participants were assigned the role of prisoner (9 plus 3 alternates), while the other 12 were assigned the role of guard (also 9 plus 3 alternates). Zimbardo took on the role of the superintendent, and an undergraduate research assistant the role of the warden. Zimbardo designed the experiment in order to induce disorientation, depersonalization, and deindividuation in the participants.

The researchers held an orientation session for guards the day before the experiment, during which guards were instructed not to physically harm the prisoners or withhold food or drink. In the footage of the study, Zimbardo can be seen talking to the guards: "You can create in the prisoners feelings of boredom, a sense of fear to some degree, you can create a notion of arbitrariness that their life is totally controlled by us, by the system, you, me, and they'll have no privacy ... We're going to take away their individuality in various ways. In general what all this leads to is a sense of powerlessness. That is, in this situation we'll have all the power and they'll have none."[10]

The researchers provided the guards with wooden batons to establish their status,[11] clothing similar to that of an actual prison guard (khaki shirt and pants from a local military surplus store), and mirrored sunglasses to prevent eye contact. Prisoners wore uncomfortable, ill-fitting smocks and stocking caps, as well as a chain around one ankle. Guards were instructed to call prisoners by their assigned numbers, sewn on their uniforms, instead of by name.

The prisoners were "arrested" at their homes and "charged" with armed robbery. The local Palo Alto police department assisted Zimbardo with the arrests and conducted full booking procedures on the prisoners, which included fingerprinting and taking mug shots. The prisoners were transported to the mock prison from the police station, where they were strip searched and given their new identities.

The small mock prison cells were set up to hold three prisoners each. There was a small corridor for the prison yard, a closet for solitary confinement, and a bigger room across from the prisoners for the guards and warden. The prisoners were to stay in their cells and the yard all day and night until the end of the study. The guards worked in teams of three for eight-hour shifts. The guards did not have to stay on site after their shift.


After a relatively uneventful first day, on the second day the prisoners in Cell 1 blockaded their cell door with their beds and took off their stocking caps, refusing to come out or follow the guards' instructions. Guards from other shifts volunteered to work extra hours, to assist in subduing the revolt, and subsequently attacked the prisoners with fire extinguishers without being supervised by the research staff. Finding that handling nine cell mates with only three guards per shift was challenging, one of the guards suggested they use psychological tactics to control them. They set up a "privilege cell" in which prisoners who were not involved in the riot were treated with special rewards, such as higher quality meals. The "privileged" inmates chose not to eat the meal in commiseration with their fellow prisoners.

After only 36 hours, one prisoner began to act "crazy", as Zimbardo described: "#8612 then began to act crazy, to scream, to curse, to go into a rage that seemed out of control. It took quite a while before we became convinced that he was really suffering and that we had to release him."

Guards forced the prisoners to repeat their assigned numbers[12] to reinforce the idea that this was their new identity. Guards soon used these prisoner counts to harass the prisoners, using physical punishment such as protracted exercise for errors in the prisoner count. Sanitary conditions declined rapidly, exacerbated by the guards' refusal to allow some prisoners to urinate or defecate anywhere but in a bucket placed in their cell. As punishment, the guards would not let the prisoners empty the sanitation bucket. Mattresses were a valued item in the prison, so the guards would punish prisoners by removing their mattresses, leaving them to sleep on concrete. Some prisoners were forced to be naked as a method of degradation. Several guards became increasingly cruel as the experiment continued; experimenters reported that approximately one-third of the guards exhibited genuine sadistic tendencies. Most of the guards were upset when the experiment concluded after only six days.

Zimbardo mentions his own absorption in the experiment. On the fourth day, some of the guards stated they heard a rumor that the released prisoner was going to come back with his friends and free the remaining inmates. Zimbardo and the guards disassembled the prison and moved it onto a different floor of the building. Zimbardo himself waited in the basement, in case the released prisoner showed up, and planned to tell him that the experiment had been terminated. The released prisoner never returned, and the prison was rebuilt in the basement.

Zimbardo argued that the prisoners had internalized their roles, since some had stated they would accept "parole" even if it would mean forfeiting their pay, despite the fact that quitting would have achieved the same result without the delay involved in waiting for their parole requests to be granted or denied.[13] Zimbardo argued they had no reason for continued participation in the experiment after having lost all monetary compensation, yet they did, because they had internalized the prisoner identity.

Prisoner No. 416, a newly admitted stand-by prisoner, expressed concern about the treatment of the other prisoners. The guards responded with more abuse. When he refused to eat his sausages, saying he was on a hunger strike, guards confined him to "solitary confinement", a dark closet: "the guards then instructed the other prisoners to repeatedly punch on the door while shouting at 416."[14] The guards said he would be released from solitary confinement only if the prisoners gave up their blankets and slept on their bare mattresses, which all but one refused to do.

Zimbardo aborted the experiment early when Christina Maslach, a graduate student in psychology whom he was dating (and later married),[15] objected to the conditions of the prison after she was introduced to the experiment to conduct interviews. Zimbardo noted that, of more than 50 people who had observed the experiment, Maslach was the only one who questioned its morality. After only six days of a planned two weeks' duration, the Stanford prison experiment was discontinued.[13]


On August 20, 1971, Zimbardo announced the end of the experiment to the participants.

The results of the experiment favor situational attribution of behavior rather than dispositional attribution (a result caused by internal characteristics). In other words, it seemed that the situation, rather than their individual personalities, caused the participants' behavior. Under this interpretation, the results are compatible with the results of the Milgram experiment, in which ordinary people fulfilled orders to administer what appeared to be agonizing and dangerous electric shocks to a confederate of the experimenter.[16]

The experiment has also been used to illustrate cognitive dissonance theory and the power of authority.

Shortly after the study was completed, there were bloody revolts at both the San Quentin and Attica prison facilities, and Zimbardo reported his findings on the experiment to the U.S. House Committee on the Judiciary.

Participants' behavior was modified due to the fact that they were watched as opposed to a lurking variable (Hawthorne effect).[17] Even knowing they were being observed, guards and prisoners acted differently than normal. Guards felt the need to show their dominance even when it was not necessary. Many of the guards' brutal behavior was changed due to the harsh environments of the prison.

The guards disrespected the prisoners in various ways. For example, they referred to prisoners by number rather than by name. It dehumanized the prisoners, which resulted in a loss of personal identity. With no control, prisoners learned they had little effect on what happened to them, ultimately causing them to stop responding, and give up.[18] Quick to realize that the guards were the highest in the hierarchy, prisoners began to accept their roles as less important human beings.

The uniforms were given to all participants to erase individual identity, and participants were randomly chosen to be either a prisoner or guard to reduce individuality.[18]

A strength of the study is that it has altered the way US prisons are run. For example, juveniles accused of federal crimes are no longer housed before trial with adult prisoners, due to the risk of violence against them.[17]


The guards and prisoners adapted to their roles more than Zimbardo expected, stepping beyond predicted boundaries, leading to dangerous and psychologically damaging situations. One third of the guards were judged to have exhibited "genuine sadistic tendencies", while many prisoners were emotionally traumatized; five of them had to be removed from the experiment early. After Maslach confronted Zimbardo and forced him to realize that he had been passively allowing unethical acts to be performed under his supervision, Zimbardo concluded that both prisoners and guards had become grossly absorbed in their roles and realized that he had likewise become as grossly absorbed in his own, and he terminated the experiment.[19] Ethical concerns surrounding the experiment often draw comparisons to a similar experiment, conducted ten years earlier in 1961 at Yale University by Stanley Milgram.[16]

Because of the nature and questionable ethics of the experiment, Zimbardo found it impossible to keep traditional scientific controls in place. He was unable to remain a neutral observer, since he influenced the direction of the experiment as the prison's superintendent. Conclusions and observations drawn by the experimenters were largely subjective and anecdotal, and the experiment is practically impossible for other researchers to accurately reproduce. Erich Fromm claimed to see generalizations in the experiment's results and argued that the personality of an individual does affect behavior when imprisoned. This ran counter to the study's conclusion that the prison situation itself controls the individual's behavior. Fromm also argued that the amount of sadism in the "normal" subjects could not be determined with the methods employed to screen them.

"John Wayne" (the real-life Dave Eshelman), one of the guards in the experiment, said the study placed undue emphasis on the cruelty of the guards, and that he caused the escalation of events between guards and prisoners after he began to emulate a character from the Paul Newman film Cool Hand Luke (1967). He further intensified his actions because he was nicknamed "John Wayne", even though he was trying to mimic actor Strother Martin, who had played the role of the sadistic Captain in the movie.[20]

What came over me was not an accident. It was planned. I set out with a definite plan in mind, to try to force the action, force something to happen, so that the researchers would have something to work with. After all, what could they possibly learn from guys sitting around like it was a country club? So I consciously created this persona. I was in all kinds of drama productions in high school and college. It was something I was very familiar with: to take on another personality before you step out on the stage. I was kind of running my own experiment in there, by saying, "How far can I push these things and how much abuse will these people take before they say, 'knock it off?'" But the other guards didn't stop me. They seemed to join in. They were taking my lead. Not a single guard said, "I don't think we should do this." ―David Eshelman[21]

Also, researchers from Western Kentucky University argued that selection bias may have played a role in the results. The researchers recruited students for a study using an advertisement similar to the one used in the Stanford Prison Experiment, with some ads saying "a psychological study" (the control group), and some with the words "prison life" as originally worded in Dr. Zimbardo's Stanford Prison Experiment. It was found that students who responded to the classified advertisement for the "prison study" were higher in traits such as social dominance, aggression, authoritarianism, etc. and were lower in traits related to empathy and altruism when statistically compared to the control group participants.[22]

The study has been criticized for demand characteristics by psychologist Peter Gray. He argues that participants in psychological experiments are more likely to do what they believe the researchers want them to do. The guards were essentially told to be cruel. However, it could be argued that it was precisely this willingness to comply with the experiment's questionable practices that showed how little was needed for the students to engage in such practices.[23]

Skeptical author Brian Dunning states:

Most of the Stanford guards did not exhibit any cruel or unusual behavior, often being friendly and doing favors for the prisoners...The statistical validity of the sample of participants, 24 male Stanford students of about the same age, has been called into question as being too small and restrictive to be generally applicable to the population at large...(and the fact that) Zimbardo has dedicated much of his career to the promotion of the idea that bad environments drive bad behavior.[24]

Guards and prisoners were playing the role of their authority, which is subjective.[17] They may have not acted the same in real life situations. In particular, the environment and authority roles they found themselves in changed their actions.

Critics contend that not only was the sample size too minimal for extrapolation, but also having all of the experimental subjects be US male students gravely undercut the experiment's validity. In other words, it's entirely conceivable that replicating the experiment using a diverse group of people (with different objectives and views in life)[17] would have produced radically distinct results; that is, had the test subjects come from divergent socio-economic and psychological groups, different experimental results may well have resulted.

Comparisons to Abu Ghraib

Lynndie England pointing to a naked prisoner being forced to masturbate in front of his captors[25]

When acts of prisoner torture and abuse at the Abu Ghraib prison in Iraq were publicized in March 2004, Zimbardo himself, who paid close attention to the details of the story, was struck by the similarity with his own experiment. He was dismayed by official military and government representatives' shifting the blame for the torture and abuses in the Abu Ghraib American military prison on to "a few bad apples" rather than acknowledging the possibly systemic problems of a formally established military incarceration system.

Eventually, Zimbardo became involved with the defense team of lawyers representing one of the Abu Ghraib prison guards, Staff Sergeant Ivan "Chip" Frederick. He was granted full access to all investigation and background reports, and testified as an expert witness in SSG Frederick's court martial, which resulted in an eight-year prison sentence for Frederick in October 2004.

Zimbardo drew from his participation in the Frederick case to write the book The Lucifer Effect: Understanding How Good People Turn Evil, published by Random House in 2007, which deals with the striking similarities between his own Stanford Prison Experiment and the Abu Ghraib abuses.[14]

Ethical issues

The experiment presented several ethical issues, the most serious of which was that the experiment continued even when participants did not wish to continue. Despite the fact that participants were told they had the right to leave at any time, Zimbardo did not allow this during the experiment.[17] Zimbardo was faced with the ethical dilemma that the experiment could possibly return outstanding results if continued, but it might also adversely affect the participants' well-being if not halted.

Currently, there are ethical guidelines to be followed.[26][27][28] The Stanford Prison Experiment led to the implementation of rules to preclude any harmful treatment of participants. Before they're implemented, human studies must now undergo an extensive review by an institutional review board (US) or ethics committee (UK) in accordance with the ethical guidelines by the American Psychological Association.[17] These guidelines review whether the potential benefit for science outweighs the possible risk for physical and psychological harm.

A post-experimental debriefing is now considered an important ethical consideration to ensure that participants are not harmed in any way by their experience in an experiment. Though Zimbardo did conduct debriefing sessions, they were several years after the Stanford Prison Experiment. By that time numerous details were forgotten; nonetheless, many participants reported that they experienced no lasting negative effects.[17] However, the debriefing process should take place immediately after an experiment to assess what psychological harm, if any, may have been done and to rehabilitate participants, if necessary.

Similar studies

BBC prison study

Psychologists Alex Haslam and Steve Reicher conducted the BBC Prison Study in 2002 and was published in 2006.[29] This was a partial replication of the Stanford prison experiment conducted with the assistance of the BBC, which broadcast events in the study in a documentary series called The Experiment. Their results and conclusions differed from Zimbardo's and led to a number of publications on tyranny, stress, and leadership. The results were published in leading academic journals such as British Journal of Social Psychology, Journal of Applied Psychology, Social Psychology Quarterly, and Personality and Social Psychology Review. The BBC Prison Study is now taught as a core study on the UK A-level Psychology OCR syllabus.

While Haslam and Reicher's procedure was not a direct replication of Zimbardo's, their study casts further doubt on the generality of his conclusions. Specifically, it questions the notion that people slip mindlessly into role and the idea that the dynamics of evil are in any way banal. Their research also points to the importance of leadership in the emergence of tyranny of the form displayed by Zimbardo when briefing guards in the Stanford experiment.[30][31]

Experiments in the United States

The Stanford prison experiment was in part a response to the Milgram experiment at Yale beginning in 1961 and published in 1963.

The Third Wave experiment was the use of authoritarian dynamics aping Nazi Party methods of mass control in a classroom setting by high school teacher Ron Jones in Palo Alto, California in 1976 with the goal of demonstrating to the class in a vivid way how the German public in World War II could have acted in the way it did.[32] Although the veracity of Jones' accounts has been questioned,[33] several participants in the study have gone on record to confirm the events.[34]

In both experiments, participants found it difficult to leave the study due to the roles they were assigned. Both studies examine human nature and the effects of authority. Personalities of the subjects had little influence on both experiments despite the test prior to the prison experiment.[35]

In the Milgram and the Zimbardo studies, participants conform to social pressures. Conformity is strengthened by allowing some participants to feel more or less powerful than others.[35] In both experiments, behavior is altered to match the group stereotype.

Physical aspects of the prison

The prison used for the experiment was a 35-foot (10.5 m) section of a basement at Stanford University. The prison had two fabricated walls, one at the entrance, and one at the cell wall to block observation. Each cell (6 x 9 feet, or 1.8 x 2.7 m), contained only a cot for the prisoners.[18] In contrast, the guards lived in a very different environment, separated from the prisoners. They were given an area for relaxation and rest, plus other comforts.

In popular culture

See also


  1. The Stanford Prison Experiment – A Simulation Study of the Psychology of Imprisonment Conducted at Stanford University
  2. FAQ on official site
  4. Intro to psychology textbooks gloss over criticisms of Zimbardo's Stanford Prison Experiment
  5. Beyond Ethics to Post-ethics: A Preface to a New Theory of Morality and Immorality, Peter Baofu
  6. The Successes and Failures of Whistleblower Laws, Robert G. Vaughan
  7. Smith, J. R.; Haslam, S. A., eds. (2012). Social Psychology: Revisiting the Classic Studies. Sage.
  8. Saletan, William (2004-05-12). "Situationist Ethics". Slate. ISSN 1091-2339. Retrieved 2016-02-02.
  9. "Slideshow on official site". p. Slide 4.
  10. "C82SAD L07 Social Influence II The BBC Prison Experiment (handout)".
  11. Haney, C.; Banks, W. C. & Zimbardo, P. G. (1973). "Research reviews" (PDF).
  12. "Slide tour". The Stanford Prison Experiment.
  13. 1 2 Zimbardo, P.G. (2007). The Lucifer Effect: Understanding How Good People Turn Evil. New York: Random House.
  14. 1 2 "The Lucifer Effect".
  15. "The Standard Prison Experiment". Stanford University News Service.
  16. 1 2 Konnikova, Maria (June 12, 2015). "The Real Lesson of the Stanford Prison Experiment". The New Yorker.
  17. 1 2 3 4 5 6 7 "Zimbardo - Stanford Prison Experiment | Simply Psychology". Retrieved 2015-11-11.
  18. 1 2 3 "Index of /downloads". Archived from the original on January 20, 2015. Retrieved 2015-11-11.
  19. "Conclusion". Stanford Prison Experiment.
  20. "'John Wayne' (name withheld) Interview: 'The Science of Evil'". Primetime: Basic Instincts. KATU. January 3, 2007.
  21. Eshelman, David (July 2011). "The Menace Within". Stanford Alumni Magazine.
  22. Carnahan, Thomas; Sam McFarland (2007). "Revisiting the Stanford prison experiment: could participant self-selection have led to the cruelty?" (PDF). Personality and Social Psychology Bulletin. 33 (5): 603–14. doi:10.1177/0146167206292689. PMID 17440210.
  23. Gray, Peter (2013). "Why Zimbardo's Prison Experiment Isn't in My Textbook". Freedom to Learn blog.
  24. "What You Didn't Know about the Stanford Prison Experiment" (Podcast). Brian Dunning. May 27, 2008. Retrieved 2014-07-15.
  25. "English-language transcript of March 2008 interview with Lynndie England". Stern magazine. 2008-03-17. Retrieved 2008-03-25.
  26. U.S. Department of Health & Human Services Code of Federal Regulations, Title 45, Part 46, Protection of Human Subjects
  27. The Belmont Report, Office of the Secretary, Ethical Principles and Guidelines for the Protection of Human Subjects of Research, The National Commission for the Protection of Human Subjects for Biomedical and Behavioral Research, April 18, 1979
  28. U.S. Department of Health and Human Services, The Nuremberg Code
  29. The BBC Prison Study Official Site
  30. Interview of Alex Haslam at The Guardian
  31. Reicher, Steve; Haslam, Alex. "Learning from the Experiment". The Psychologist (Interview). Interview with Briggs, Pam. Archived from the original on 2009-02-21.
  32. Jones, Ron (1976). "The Third Wave". The Wave Home. Archived from the original on 2015-02-02. Retrieved 2016-12-03.
  33. "several email exchanges with former students". Archived from the original on 2013-01-27. Retrieved 2016-12-03.
  34. "A Look at the Original Students of The Third Wave and Their Teacher Ron Jones, 40 Years Later"
  35. 1 2 "Comparing Milgram's Obedience and Zimbardo's Prison Studies". PSY 101 - Introduction to Psychology by Jeffrey Ricker, Ph.D. Retrieved 2015-11-12.
  36. Wolfe, Gene (1975). When I was Ming the Merciless.
  37. "Quiet Rage: The Stanford Prison Experiment (1992 documentary)". Justice videos.
  38. Highfill, Samantha (July 17, 2015). "Billy Crudup turns college students into prison guards in The Stanford Prison Experiment". Entertainment Weekly.


External links

Abu Ghraib and the experiment:

This article is issued from Wikipedia - version of the 12/4/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.