A critical evaluation of the dispositional hypothesis, however, cannot be made directly through observation in existing prison settings, since such naturalistic observation necessarily confounds the acute effects of the environment with the chronic characteristics of the inmate and guard populations. To partial out the situational effects of the prison environment per se from those attributable to a priori dispositions of its inhabitants requires a research strategy in which a “new” prison is constructed, comparable in its fundamental social-psychological milieu to existing prison systems but entirely populated by individuals who are undifferentiated in all essential dimensions from the rest of society.
Such was the approach taken in the present empirical study, namely, to create a prisonlike situation in which the guards and inmates were initially comparable and characterized as being “psychologically healthy,” and then to observe the patterns of behavior which resulted and to record the cognitive, emotional, and attitudinal reactions that emerged.
No specific hypotheses were advanced other than the general one that assignment to the treatment of “guard” or “prisoner” would result in significantly different reactions on behavioral measures of interaction, emotional measures of mood state and pathology, and attitudes toward self, as well as other indices of coping and adaptation to this extreme situation.
Method
The effects of playing the role of “guard” or “prisoner” were studied in the context of an experimental simulation of a prison environment. The research design was a relatively simple one, involving as it did only a single treatment variable, the random assignment to either a “guard” or “prisoner’’ condition. These roles were enacted over an extended period of time (nearly one week) within an environment which had been physically constructed to closely resemble a prison. Central to the methodology of creating and maintaining the psychological state of imprisonment was the functional simulation of significant properties of “real prison life” (established through information from former inmates, correctional personnel, and texts).
Subjects
The 22 subjects who participated in the experiment were selected from an initial pool of 75 respondents who answered a newspaper ad asking for male volunteers to participate in a psychological study of “prison life,” in return for payment of $15 per day. Those who responded to the notice completed an extensive questionnaire concerning their family background, physical and mental health history, prior experience, and attitudinal propensities with respect to any possible sources of psychopathology (including their involvements in crime). Each respondent who completed the background questionnaire was interviewed by one of two experimenters. Finally, the 24 subjects who were judged to be most stable (physically and mentally) were selected to participate in the study. On a random basis, half of the subjects were assigned the role of “guard,” half were assigned to the role of “prisoner.”
The subjects were normal, healthy males attending colleges throughout the United States who were in the Stanford [University] area during the summer. They were largely of middle-class background and Caucasians (with the exception of one Asian subject). Initially they were strangers to each other, a selection precaution taken to avoid the disruption of any preexisting friendship patterns and to mitigate against any transfer of previously established relationships or patterns of behavior into the experimental situation.
Procedure
Role Instructions
All subjects had been told that they would be randomly assigned either the guard or the prisoner role, and all had voluntarily agreed to play either role for $15 per day for up to two weeks. They signed a contract guaranteeing a minimally adequate diet, clothing, housing, and medical care, as well as the financial remuneration, in return for their stated “intention” of serving in the assigned role for the duration of the study.
It was made explicit in the contract that those assigned to be prisoners should expect to be under surveillance (have little or no privacy) and to have some of their basic civil rights suspended during their imprisonment. They were aware that physical abuse was explicitly prohibited. Subjects were given no other information about what to expect and no instructions about behavior “appropriate” for the prisoner role. Those actually assigned to this treatment were informed by phone to be available at their place of residence on a given Sunday, when we would start the experiment.
The subjects assigned to be guards attended an orientation meeting on the day prior to the induction of the prisoners. At this time they were introduced to the principal investigators, the “superintendent” of the prison (P.G.Z.) and an undergraduate research assistant who assumed the administrative role of “warden.” They were told that we were attempting to simulate a prison environment within the limits imposed by pragmatic and ethical considerations. Their assigned task was to “maintain the reasonable degree of order within the prison necessary for its effective functioning,” although the specifics of how this duty might be implemented were not explicitly detailed. To involve the subjects in their roles even before the first prisoner was incarcerated, the guards assisted in the final phases of completing the prison complex—putting the cots in the cells, posting signs on the walls, setting up the guards’ quarters, and moving furniture, water coolers, and refrigerators.
The guards generally believed that we were interested primarily in studying the behavior of prisoners. Of course, we were also concerned with effects which enacting the role of guard in this environment would have on their behavior and subjective states. For this reason, they were given few explicit instructions on what it meant to be a guard and were left to “fill in” their own definitions of the role. A notable exception was the explicit and categorical prohibition against the use of physical punishment or aggression, which we emphasized from the outset of the study.
The prisoner subjects remained in the mock prison 24 hours a day for the duration of the study. Three were arbitrarily assigned to each of the three cells, and two others were on standby call at their homes. The guard subjects worked on three-man, eight-hour shifts, remaining in the prison environment only during their work shifts and going about their usual routines at other times. The one subject assigned to be a standby guard withdrew just before the simulation phase began. Final data analysis, then, is based on 11 prisoners and 10 guards.
Physical Aspects of the Prison
The prison was built in a 35-foot section of a basement corridor in the psychology building at Stanford University. It was partitioned by two fabricated walls, one of which was fitted with the only entrance door to the cell block; the other contained a small observation screen. Three small cells (6 × 9 feet) were made from converted laboratory rooms by replacing the usual doors with steel-barred doors painted black and removing all furniture. A cot (with mattress, sheet, and pillow) for each prisoner was the only furniture in the cells. A small closet across from the cells served as a solitary confinement facility; its dimensions were extremely small (2 × 2 × 7 feet), and it was unlit.
In addition, several rooms in an adjacent wing of the building were used as guards’ quarters (to change in and out of uniform or for rest and relaxation), a bedroom for the “warden” and “superintendent,” and an interview-testing room. Concealed video recording equipment was located in the testing room and behind the observation screen at one end of the “yard,” where there was also sufficient space for several observers.
Uniforms
In order to promote feelings of anonymity in the subjects, each group was issued uniforms. For the guards, this consisted of plain khaki shirts and trousers, a whistle, a police nightstick (wooden baton), and reflecting sunglasses which made eye contact impossible. The prisoners’ uniforms were loosely fitting muslin smocks with an identification number on front and back. A light chain and lock were placed around one ankle. On their feet they wore