40 Years Later: The Stanford Prison Experiment

Male college students needed for psychological study of prison life. $15 per day for 1-2 weeks.

Forty years ago one of the most notorious experiments in social psychology, the Stanford Prison Experiment (SPE), was underway. Led by psychologist Philip Zimbardo and funded by the U.S. Office of Naval Research, the study sought to “understand the…effects of roles, labels, and social expectations” in a simulated prison environment.

More than 70 students responded to the ad for the study. Zimbardo’s team interviewed all applicants, eliminating candidates with psychological problems, criminal backgrounds, or histories of drug abuse. The students selected were to spend two weeks in a basement that had been modified into a “prison.” They were each randomly assigned a role: prisoner or guard.

The nine “prisoners” were arrested at their homes, processed at the police station, and taken to the mock prison, where they were issued prison smocks and ankle chains and assigned ID numbers. Among the rules established (PDF), prisoners were to address each other only by ID number. Guards donned military-style khaki uniforms, batons, and mirrored sunglasses (to prevent eye contact). Their primary directive was to maintain order in the prison, without resorting to physical violence. All were instructed to immerse themselves in the experiment completely.

The first night passed without incident. On the second day, the three prisoners in cell 1 initiated a riot. The night-shift guards were called in and broke the riot up by attacking with fire extinguishers. Order was restored and the prisoners who had not participated in the riot were offered special privileges—a psychological tactic employed to divide the inmates. Over the course of the experiment punishments escalated to include refusal of toilet privileges, forcing the inmates to sleep on their cell floors, “solitary confinement” within an unlit closet (inflicted upon one prisoner who attempted a hunger strike), stripping the men nude, and general acts of humiliation. Inmates were made to count off repeatedly in order to learn their numbers, with errors in the count earning physical punishment. Thirty-six hours into the simulation, prisoner #8612 began to appear dangerously affected. On the fourth day, some inmates began to plot an escape. Worried parents, who had seen their sons during "visiting hours," implored Zimbardo to release their sons; some of the most emotionally disturbed were finally granted “parole.” When things got really out of hand and Zimbardo attempted to move the prisoners to the more secure local police station, city officials told him they would no longer cooperate with his experiment.

Zimbardo’s hypothesis was that individuals will conform, against their nature, to roles of authority and submission. He hoped the study would illuminate how an individual (the prisoner) adapts to being in a powerless situation–the guards were initially only of interest for their role in the prisoners’ transformations.

In fact, both guards and prisoners fell into their roles so quickly and dramatically that the experiment was ended after only six days. Half the inmates had already been released due to severe emotional reactions, and the investigators had determined that one-third of the guards were exhibiting genuine sadistic tendencies. Zimbardo himself had participated—as prison superintendent—and admitted to losing sight of his role as psychologist and permitting the abuse of the prisoners to carry on too long. On August 20, 1971, he called all SPE participants to a meeting and announced that the study was terminated, the prison shutting down. It was later reported that some of the guards were disappointed to see the experiment end early. Many have since expressed remorse for and shock at their behavior.

Zimabaro has said that he expected they would “write some articles about it and move on,” but the experiment drew considerable public interest—and criticism—at the time. While the study had been approved by Stanford's Human Subjects Research Committee, and a 1973 investigation by the American Psychological Association (APA) determined the experiment to be ethically sound, Zimbardo’s contemporaries criticized his methodology. Subsequent years saw revisions to APA guidelines that would prevent similar human-based simulation experiments. As Zimabardo said, "No behavioral research that puts people in that kind of setting can ever be done again in America."

–Sarah King

For more background:

Stanford Prison Experiment: A Simulation Study of the Psychology of Imprisonment Conducted at Stanford University. The official website of the experiment including a slideshow, FAQ, and documentation.

The Menace Within” Zimardo and others involved reflect on the experiment in Stanford’s alumni magazine.

The official SPE YouTube page. Including footage from the experiment.

Psychologist Erich Fromm’s criticism of the study.


3 responses

  1. This is all wrong. Zimbardo didnt go to the local police station adn the parents were not displeased, Zimbardo actually played music over the intercom and allowed the prisoners to see them for 10 minutes and kept it to minimum. Please dont listen to these people

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