In the early 1970s, Craig Haney, Curt Banks, Carlo Prescott, and Philip Zimbardo conducted a landmark situational study at Stanford University. The experiment tested the fundamental attribution error: our tendency to attribute causes of behavior to personal factors, underestimating the influence of situational conditions.
For this study, a small group of college students volunteered to be subjects and were carefully tested for sound psychological and physical health. Half of the students were randomly selected to act as prisoners, the other half to act as guards. The study took place in a simulated jail facility in the Stanford University Psychology Department.
Once the study subjects entered the simulated jail, uniforms, rules, and other details distinguished the two groups from each other, and blurred the line between the reality of the study and life in prison. The students spent much of the day cramped in tiny cells, undergoing physical trials, and enduring the overall claustrophobic atmosphere of a small jail 24 hours a day. The guards, however, were allowed to return to their homes and normal surroundings after their shifts.
What happened during the study, originally planned to last two weeks, was more dramatic than anyone had anticipated, even the researchers themselves. (Excerpt from learner.org)