Zimbardo Prison Experiment: Psychology of Power and Evil

Introduction

The Zimbardo Stanford Prison Experiment was legendary in its time and remains extremely relevant today. The study, performed over one week during the summer of 1971, indicates that a psychology of good and evil exists in the prison environment, and it can lead to stress, psychopathic behavior, and violence even in those not normally prone to violence.

Study Design and Prison Setup

The study began with newspaper advertisements recruiting college students to act as prisoners for two weeks. Twenty-four applicants were ultimately approved. They were divided randomly into two groups: guards and prisoners. The actual "prison" was constructed in the basement of the university psychology building and contained cells and a "yard" — actually a corridor — where prisoners could exercise once each day. The researchers consulted law enforcement officers, ex-convicts, and other experts to make the prison experience as realistic as possible. The cells looked remarkably authentic and even included a "hole," or solitary confinement cell, for prisoners who misbehaved. The prison was equipped with video cameras so researchers could record all activity, and an intercom system allowed them to make prison-wide announcements as well as to listen in on conversations that guards and prisoners believed were private. There were no windows or clocks, which created an illusion of altered time and appeared to amplify the overall results of the experiment.

The prisoners were arrested by surprise and were blindfolded during their transport to the mock prison — a tactic that resembles methods of psychological intimidation. As part of the booking process, prisoners were stripped naked, searched, and sprayed with an insecticide to "delouse" them. Prisoners wore identical smock-style uniforms with no underwear, a chain on one ankle, and a stocking cap fashioned from a woman's nylon stocking. They had no identity beyond the prison numbers stenciled on the front and back of their smocks. Zimbardo makes clear that the intent of the treatment and uniforms was to humiliate and degrade the prisoners so that guards could maintain control. He notes in the study, "Real male prisoners don't wear dresses, but real male prisoners do feel humiliated and do feel emasculated. Our goal was to produce similar effects quickly by putting men in a dress without any underclothes" (Zimbardo). Although the prisoners had expected some harassment when they volunteered, it quickly became clear that a large gap was widening between the prisoners — who had no power — and the guards, who wielded all of it.

The guard volunteers received no training and were free to devise their own rules of conduct. A graduate student acting as warden supervised them. The guards carried a whistle and a billy club but no firearms, and wore identical uniforms and mirrored sunglasses so that prisoners could not see their eyes or read their emotions. The initial study began with nine guards and nine prisoners. Prisoners remained in cells 24 hours a day while three guards worked three eight-hour shifts. The remaining volunteers were on call if needed. Three prisoners shared each of three cells, which were so small they contained only three sleeping cots and little else. Throughout the experiment, guards frequently conducted counts, waking prisoners at odd hours of the night to assert authority, and implemented punishments for misbehavior or inappropriate reactions to guard power.

Guard Tactics and the Prisoner Rebellion

After only one day and night of this treatment, the prisoners rebelled. They removed parts of their required uniform — the identification numbers and stocking caps — barricaded their cell doors with cots, refused to come out, and taunted the guards. The morning shift of guards did not know how to respond and blamed the night shift for allowing the situation to develop. They called in backup from the on-call pool and kept the night shift on duty as well to help suppress the riot. To reassert control, the guards doused prisoners with fire extinguishers, forced open the cells, stripped the prisoners naked, removed their cots, and placed the ringleaders in solitary confinement. They then harassed the remaining prisoners to demonstrate they were back in charge.

Recognizing that nine guards could not remain on duty simultaneously, the guards developed psychological tactics to maintain control. They designated a "privilege" cell for the prisoners least involved in the riot and most cooperative with the guards. These prisoners were allowed to keep their uniforms and beds, wash, brush their teeth, and receive regular meals — privileges denied to the remaining prisoners, including food. In this way, the guards drove a deliberate wedge between "good" and "bad" prisoners. After a few days, the guards swapped the two groups, which deepened confusion and reinforced the guards' authority. One law enforcement consultant noted that this was a tactic used in many real prison situations. Zimbardo observed, "In fact, in a real prison the greatest threat to any prisoner's life comes from fellow prisoners. By dividing and conquering in this way, guards promote aggression among inmates, thereby deflecting it from themselves" (Zimbardo). The rebellion ultimately fractured the prisoners while drawing the guards closer together, further consolidating their power.

Only 36 hours into the experiment, one prisoner "broke" and exhibited signs of "acute emotional disturbance, disorganized thinking, uncontrollable crying, and rage" (Zimbardo). The researchers initially believed the prisoner was attempting to manipulate them into releasing him, because the prison mentality had already taken hold of everyone involved. It took a full breakdown before the researchers recognized he was not faking, and they released him.

When a rumored escape plot emerged, the researchers — rather than allowing it to unfold as a natural development in the study — became so immersed in the prison mentality that they actively worked to prevent the escape and secure the facility. Zimbardo notes, "What we did was to hold a strategy session with the Warden, the Superintendent, and one of the chief lieutenants, Craig Haney, to plan how to foil the escape" (Zimbardo). They even planted an informant among the prisoners. An independent colleague who visited the study asked about the "independent variable," and this single question helped the researchers recognize how far they had strayed from scientific objectivity. They had become part of the prison system rather than impartial observers. When the escape failed to materialize, the guards retaliated against the prisoners. More prisoners broke down and could no longer distinguish the simulation from reality.

Conclusion

The Zimbardo prison study was remarkable for a number of reasons. First, it lasted only six days yet is still studied and cited today. It demonstrated how quickly the human mind assimilates to new and stressful situations, how people cope with those situations, and how power can corrupt individuals with startling speed. The lessons drawn from this experiment remain entirely valid. They show that with the right conditions, power and control can generate evil and dominance within the human mind — a pattern that extends from Nazi concentration camps to the abuses at Abu Ghraib. There is a capacity for evil in many people, and it tends to emerge precisely when it can do the most damage. The study is, ultimately, a frightening window into human behavior and the speed with which institutions of confinement corrupt and harm those inside them.