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 rubber sandals, and their hair was covered with a nylon stocking made into a cap. Each prisoner was also issued a toothbrush, soap, soapdish, towel, and bed linen. No personal belongings were allowed in the cells. The outfitting of both prisoners and guards in this manner served to enhance group identity and reduce individual uniqueness within the two groups.
Induction Process
With the cooperation of the Palo Alto City Police Department, all of the subjects assigned to the prisoner treatment were unexpectedly “arrested” at their residences. A police officer charged them with either suspicion of burglary or armed robbery, advised them of their legal rights, handcuffed them, thoroughly searched them (often as curious neighbors looked on), and carried them off to the police station in the rear of the police car. At the station they went through the standard booking routines of being fingerprinted, having an identification file prepared, and then being placed in a detention cell. Subsequently, each prisoner was blindfolded and driven by one of the experimenters and a subject-guard to our mock prison. Throughout the entire arrest procedure, the police officers involved maintained a formal, serious attitude, avoiding answering any questions of clarification as to the relation of this “arrest” to the mock prison study.
Upon arrival at our experimental prison, each prisoner was stripped, sprayed with a delousing preparation (deodorant spray), and made to stand alone, naked, in the cell yard before being outfitted. After being given their uniforms and having an I.D. picture (“mug shot”) taken, each prisoner was put in his cell.
Administrative Routine
When all the cells were occupied, the warden greeted the prisoners and read them the rules of the institution (developed the previous day by the guards and the warden). They were to be memorized and to be followed. Prisoners were to be referred to only by the number of their uniforms, in a further effort to depersonalize them.
The prisoners were served three bland meals per day, were allowed three supervised toilet visits, and were given two hours daily for the privilege of reading or letter writing. Work assignments were issued for which the prisoners were to receive an hourly wage to constitute their $15 daily payment. Two visiting periods per week were scheduled, as were movie rights and exercise periods. Three times a day all prisoners were lined up for a “count” (one on each guard work-shift). The initial purpose of the count was to ascertain that all prisoners were present and to test them on their knowledge of the rules and of their I.D. numbers. The first perfunctory counts lasted only about 10 minutes, but on each successive day (or night) they were spontaneously increased in duration by the guards until some lasted several hours. Many of the preestablished features of administrative routine were modified or abandoned by the guards, and some privileges were forgotten by the staff over the course of study.
Data Collection: Dependent Measures
The exploratory nature of this investigation and the absence of specific hypotheses led us to adopt the strategy of surveying as many behavioral and psychological manifestations of the prison experience on the guards and the prisoners as was possible. The dependent measures were of two general types: (1) transactions between and within each group of subjects, recorded on video- and audiotape as well as directly observed, and (2) individual reactions on questionnaires, mood inventories, personality tests, daily guard shift reports, and postexperimental interviews.
Data collection was organized around the following sources:
1 Videotaping Using the concealed video equipment, about 12 hours of recordings were made of daily, regularly occurring events such as the counts and meals, as well as unusual interactions such as a prisoner rebellion; visits from a priest, a lawyer, and parents; parole board meetings; and others.
2 Audio recording Concealed microphones recorded over 30 hours of verbal interactions between guards and prisoners in the prison yard, as well as some within the cells and in the testing-interview room.
3 Rating scales Mood adjective checklists and sociometric measures were administered on several occasions to assess emotional changes in affective state and interpersonal dynamics among the guard and prisoner groups.
4 Individual difference scales Prior to the start of the simulation, all subjects had completed a series of paper-and-pencil personality tests selected to provide dispositional indicators of interpersonal behavior styles—the F scale of Authoritarian Personality (Adorno, Frenkel-Brunswik, Levinson, and Sanford 1950) and the Machiavellianism Scale (Christie and Geis 1970)—and to isolate areas of possible personality pathology through the newly developed Comrey Personality Scale (Comrey 1970).
5 Personal observations The guards made daily reports of their observations after each shift, the experimenters kept informal diaries, and all subjects completed postexperimental questionnaires of their reactions to the experience about a month after the study was over.
Data Analysis: Video Recordings
Special analyses were required only of the video and audio material. The other data sources were analyzed following established scoring procedures.
Since the present discussion is based primarily on the videotaped material, details of this analysis are outlined here.
There were 25 relatively discrete incidents identifiable on the tapes of prisoner–guard interactions. Each incident or scene was scored for the presence of nine behavioral (and verbal) categories by two judges who had not been involved with the simulation study. These
