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Zimbardo's Prison Study

In 1975, social psychologist Philip Zimbardo conducted an experiment demonstrating that violent and aggressive behavior could be elicited from typical college students simply by asking them to act in the role of a prison guard. Zimbardo was curious about the psychological effects of imprisonment, so he arranged for students to enact the roles of prisoners or prison guards. Male subjects were recruited through newspaper ads offering them $15 a day to participate. Seventy-five men applied to participate, and 19 were chosen. A battery of tests was employed to select those with the most stable personalities. Volunteers were randomly assigned to play prison guard or prisoner through the flip of a coin.

What was Zimbardo's prison study?

The preparation and execution of the study was amazingly thorough and realistic. It began on a Sunday morning as police swept through Palo Alto, the home of Stanford University, picking up the students who had been selected as prisoners. The sirens blared as students who had been tapped to play the prisoner role were arrested, placed spread-eagled against a car, searched, handcuffed, and booked at the police station. After some fingerprinting and paperwork, the prisoners were transported to Stanford County Prison, which was actually the basement of the Stanford psychology building, unused in the weeks after summer term.

The prisoners were stripped and their hair was sprayed to kill lice. They were required to stand naked and listen to the guards read a list of rules and regulations. One of the rules was that prisoners had to follow any order from a guard. Another rule was that they had to ask for permission to do anything, even to go to the toilet. After this the prisoners were issued a simple uniform and a towel and each was assigned to a cell.

What elements helped make the prison study realistic?

The guards in the study were given khaki-colored uniforms and mirrored sunglasses, so they had an anonymous and sinister look. They wore billy clubs, keys, and handcuffs. They received no special instructions from Zimbardo. He just told them to play the role of prison guards and to maintain order in the mock prison.

How did the prison guards start to act?

Before long, the prison guards were acting mean. For example, they decided to call roll during the middle of the night and make the prisoners do pushups, with guards putting their feet on the middle of a prisoner's back. On the second day of the experiment, the guards crushed a rebellion and became more verbally abusive.

What were the reactions of prisoners?

After a day and a half, one of the prisoners had to be released because of uncontrolled crying, depression, fits of rage, and disorganized thinking. A few days later, the same thing happened to three additional prisoners. By the fifth day, all the volunteer prisoners asked to be released from the experiment, even though it meant they would forfeit their pay. One subject developed a skin rash over his whole body after having his appeal rejected by a mock Parole Board. On the sixth day the experiment was terminated because "the experience dramatically and painfully transformed most of the participants in ways we did not anticipate, prepare for, or expect" (Haney & Zimbardo, 1998).

Zimbardo noted that every single student playing the guard role became authoritarian and abusive at least once, and many of them seemed to enjoy the role. Although Zimbardo did not tell the guards to act aggressive, evidently they felt this was part of the prison guard role or stereotype. Perhaps they had gotten this idea from watching old movies. Whatever the reason, they willingly acted the role.

What are some things the prison study had in common with Milgram's obedience study?

The Zimbardo prison study resembles the Milgram obedience study in several ways. It put ordinary citizens in the role of torturers or bullies, in part by appearing to remove their personal responsibility for their actions. The Zimbardo research, like the Milgram study, raised protests about abusive treatment of experimental subjects. However, like Milgram, Zimbardo exercised extraordinary care in debriefing his subjects and conducting follow-up interviews to make sure none suffered lasting harm. The Zimbardo prison study, like the Milgram study, was valuable in showing how easily ordinary people could slip into a brutal and aggressive pattern of behavior, especially if it was approved by an authority.

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