How the Stanford Prison Experiment Worked

The Takeaways

Zimbardo poses in front of posters for the 2015 movie Taylor Hill/FilmMagic/Getty Images

Zimbardo realized that rather than a neutral scenario, he created a prison much like real prisons, where corrupt and cruel behavior didn't occur in a vacuum, but flowed from the rules and principles of the institution to the people who carried out those principles. The behavior of the guards and prisoners wasn't dictated by some inherent internal trait, but by the situation they were in. The theory that external circumstances are the primary drivers of human behavior is known as situationist theory. Zimbardo didn't form the theory, but his experiment and later writings helped popularize it.

Experimental ethics are also an issue to consider. The Stanford Human Subjects Review Committee and Zimbardo's superiors approved the experiment — another layer of authority complicit in the experiment's outcome (it's like situationist "Inception") — but experimental ethics are more rigorous today. A modern institutional review board would likely never approve such an experiment without major modifications. Zimbardo has said that he feels the initial experiment was ethical (all the participants understood what they'd signed up for and consented), but that he suffered an ethical lapse when he allowed it to continue beyond the first emotional breakdown of a prisoner [source: Stanford Prison Experiment].


The idea that humans have an inherent tendency toward abuse of authority and submission to authority is not ruled out by the experiment, however. The Stanford Prison Experiment is closely related to another psychological experiment that's as infamous: Stanley Milgram's obedience to authority experiment. In fact, Zimbardo and Milgram were high school classmates and colleagues at Yale University. In the obedience experiment, volunteers were directed to press buttons delivering increasingly powerful, and eventually fake lethal shocks to another person at the direction of a researcher. A large percentage of volunteers went along with the researcher's demands. However, like the Stanford Prison Experiment, the ethics, methodology and conclusions of Milgram's experiment have been called into question recently. And both experiments influenced changes in the regulation and ethical guidelines of studies with human subjects [sources: Zimbardo et al., Defiesta].

Zimbardo's conclusion was that we are not so much inherently "evil," but that we will commit heinous acts if encouraged to do so by systems that enable or encourage them. He took his results to the U.S. House of Representatives shortly after the experiment ended, testifying before a subcommittee on prison reform. His primary argument was that given the power institutions have to dictate the behavior of the people within them, it's necessary to reform those institutions to avoid those abuses. He suggested better training and pay for guards, better protection for prisoners' human rights, and specific training programs that could include role-playing scenarios to help guards learn to deal humanely with prisoners (and weed out the most sadistic among guards) [source: House of Representatives]. The 2003 scandal surrounding prisoner treatment at the Iraqi prison Abu Ghraib, which mirrored the actions of Zimbardo's guards in disturbing ways, suggests that the experiment is not a relic of the past but still relevant to the way people are treated in modern civilian and military prisons.

Zimbardo's testimony also reflected his belief that researchers should not remain impartial observers, but should engage in social and political ways to act on the discoveries they make and seek ways to improve the world [source: Zimbardo et al.].

Author's Note: How the Stanford Prison Experiment Worked

Much of the appeal of the Stanford Prison Experiment, aside from the dark, voyeuristic thrill of learning how the subjects acted, is how easily it lets you insert yourself into the narrative Zimbardo created. What kind of guard would you be? How would you react when another guard did something sadistic? How would you react as a prisoner? Would you organize your fellow prisoners, or work against them to gain favor with the guards? Or maybe you envision yourself in Zimbardo's position, pulling the strings in your scenario. How would you have changed the conditions to alter the subjects' behavior? Could you redesign the experiment to be more ethical?

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More Great Links


  • Carnahan, Thomas et al. "Revisiting the Stanford Prison Experiment: Could Participant Self-Selection Have Led to the Cruelty?" Personality and Social Psychology Bulletin. Vol. 33, issue 5. May 1, 2007. (June 22, 2017)
  • Defiesta, Nick. "When Psychologists 'Go Wrong.'" Yale Daily News. Sept. 28, 2011. (July 14, 2017)
  • Haney, Craig et al. "Interpersonal Dynamics in a Simulated Prison." International Journal of Criminology and Penology. 1973. (June 10, 2017)
  • House of Representatives. "Hearings Before Subcommittee No. 3 of the Committee on the Judiciary, House of Representatives, Ninety-Second Congress, First Session on Corrections Part 2, Prisons, Prison Reform, and Prisoner Rights: California." Oct. 25, 1971. (June 12, 2017)
  • Konnikova, Maria. "The Real Lesson of the Stanford Prison Experiment." The New Yorker. June 12, 2015. (June 12, 2017)
  • Ratnesar, Romesh. "The Menace Within." Stanford Magazine. July/August 2011. (July 14, 2017)
  • Reicher, Stephen & S. Alexander Haslam. "Rethinking the psychology of tyranny: The BBC prison study." British Journal of Social Psychology. 2006. (June 12, 2017)
  • Sedacca, Matthew. "The Man Who Played With Absolute Power." Feb. 16, 2017. (July 6, 2017)
  • Stanford Prison Experiment. "The Story." (June 12, 2017)
  • Zimbardo, Philip G. "A Situationist Perspective on the Psychlogy of Evil." "The Social Psychology of Good and Evil," Gilford Press. 2004. (June 12, 2017)
  • Zimbardo, Philip G. et al. "Reflections on the Stanford Prison Experiment: Genesis, Transformations, Consequences." In T. Blass (Ed.),"Obedience to Authority: Current Perspectives on the Milgram Paradigm" (pp. 193-237). Lawrence Erlbaum Assoc. 2000. (June 12, 2017)