A study of prisoners and guards in a simulated prison - Haney, C., Banks, C. and Zimbardo, P. (1973)


To show how the taking of social roles would lead to excessive conformity to those roles.
To test the dispositional hypothesis.


The participants consisted of twenty-four men that were considered physically and mentally stable, mature, and the least involved in antisocial behavior. They were all college students, white, middle class, male, healthy.

Research Method

The research method used in this study was a Field experiment.


Participants were randomly assigned to be a prisoner or a guard. As the researchers wanted to make this experiment as real as possible, police cars arrived at the participants’ houses and arrested them. They were then fingerprinted and blindfolded, searched, stripped naked, and deloused, as any real prisoner would have to do. The prisoners were given their uniforms, which consisted of a smock with a number printed on it, a cap, and a chain around their ankle. Guards were given a uniform which consisted of khaki shirts and pants, reflective sunglasses, and batons. Prisoners stayed in the prison and followed a strict schedule which consisted of work assignments, rest, and toilet and food breaks. The guards worked in eight hour shifts. SPECIAL EQUIPMENT/MATERIALS:
The simulated prison: 3 6”9 cells: 3 prisoners to a cell, a cot (with mattress, sheet, and pillow) for each prisoner Solitary confinement: ‘The Hole’ a very small, unlit room (2 x 2 x 7 ft) across from cells. Guard’s quarters: Rooms in an adjacent wing used to change in and out of uniform and for relaxation, interview rooms and a bedroom for the ‘warden and superintendent’ (Zimbardo) The Yard: A small, enclosed room To recreate a real prison the researchers consulted a former prisoner. An intercom system was installed. No clocks or windows. Uniforms:
-Made to fit the roles of the participants.
-Prisoners had loose fitting smocks, containing ID numbers.
-Prisoners were to wear chains around their ankles, along with caps on their hair.
The effect the uniforms had on the participants was they were able to identify with their roles in a more realistic way. If the participants were dressed as prisoners, they would in turn begin to feel like prisoners, resulting in prisoner behavior.nue. You have no other choice, you must go on.


The experiment ended rather quickly. It ended after just 6 days instead of the planned 14 says because of the pathological reaction of participants. 5 prisoners had to be released early due to extreme emotional depression. The guards ended up humiliating and punishing the prisoners which led the prisoners to show signs of mental and emotional distress. On the second day the prisoners organized a revolt and riot due to the living conditions and the guards worked extra hours and developed a plan to stop the riot using, fire extinguishers. After the second day the prisoners began to feel helpless and no longer in control of their lives. Eventually the guards became more aggressive and abusive. Many seemed to really enjoy the power and control that came along with the uniform. Some even volunteered to work extra shifts. The even continued to behave so aggressively even when they thought the cameras were not on. The prisoners’ rights were became privileges and they were punished with little or no justification.The prisoners became institutionalized very quickly and adapted to their roles. There was evidence of Pathological Prisoner Disorder, which includes the loss of personal identity (the prisoners ID numbers), the arbitrary control exercised by the guards, dependency and emasculation. One prisoner left and a replacement prisoner was introduced. He went on a hunger strike in protest about the treatment of inmates and as an attempt to be released. The other inmates saw him as a troublemaker instead of a victim trying to help.

Ecological Validity

The validity of this experiment is often criticized:
  • This study was a field experiment rather than a scientific experiment which meant there was only observational results but no scientific evaluation.
  • Experiment conditions are difficult to replicate.
  • Subjects were selected and paid- this may have created a pre-disposition towards their violent force. Only male subjects were studied.

  • However, the study was able to maintain some degree of control.
  • Participants were chosen in “healthy conditions”. Guards and prisoners were randomly assigned to their roles.
  • Realistic setting of prison made it seem as a true scenario.
  • Experiment took place in Stanford University; due to it’s prestige, the validity of the results and experiment itself are less likely to be questioned.
  • Explanations

    The study rejects the dispositional hypothesis.
    The prison environment was an important factor in creating the guards’ brutal behavior which none of them showed before the study. People will readily conform to the social roles they are expected to play, especially if the roles are strongly stereotyped as the guards were.
    The roles that people play shape their attitudes and behavior.
    If it only took six days to change the behavior of the participants in the study, imagine the greater effects in real life.


  • High levels of control
  • Realistic setting made it easier for participants to portray their role.
  • Uniforms enabled participants to identify themselves as their role.
  • Roles were randomly assigned.
  • Data was collected through many forms of qualitative approaches.

  • Weaknesses

    One weakness of this study is that the participants were being paid to be in the study, so their is a possibility they were purposefully acting a certain way to try and help the experimenters. Another weakness of this study is that many considered it to be very unethical, as the subjects faced extreme emotional distress and some were not allowed to leave right away as they had requested.


  • The study was approved by the Office of Naval Research.
  • The only deception was the arrests.
  • They signed consent forms.
  • Extensive group and individual debriefings were held.
  • Zimbardo listened to the advice of other psychologists.
  • Zimbardo stopped early.
  • The information gained was worth it.
  • There may have been researcher bias since Zimbardo played the warden.
  • Prisoners were deprived of their rights; searched, stripped naked, and deloused.
  • Toilet facilities became a privilege, access to the bathroom was frequently denied.Prisoners were often stripped and subjected to humiliation, as a weapon of intimidation.
  • Haney, C., Banks, C. and Zimbardo, P. (1973)

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