The Stanford Prison Experiment

• The SPE - aim

  Zimbardo set up a mock prison in the basement of the psychology department at Stanford University to test whether the brutality of prison guards was the result of sadistic personalities or whether it was created by the situation.
• The SPE - procedure

  They recruited 24 'emotionally stable' students (determined by a psych. eval.). They were also randomly assigned the role of guard or prisoner.

  To increase realism prisoners were arrested in their homes and delivered to the prison - blindfolded, strip-searched, deloused, and issued a uniform and number.

  The prisoners' daily routines were heavily regulated. Use of deindividuation:

  • Prisoners' names were never used, only their numbers.
  • Guards had their own uniform - wooden club, handcuffs, keys and mirror shades. They were told they had complete power over the prisoners.
• The SPE - findings

  Within two days, the prisoners rebelled against their treatment. They ripped their uniforms and shouted and swore at the guards, who retaliated with fire extinguishers.

  Guards harassed the prisoners constantly by conducting frequent headcounts, sometimes in the middle of the night.

  Guards highlighted the differences in social roles by creating opportunities to enforce the rules and punish slight misdemeanours.

  The guards' behaviour threatened the prisoners' physical and mental health, the study was stopped after 6 days instead of the planned 8.
• The SPE - conclusion

  The simulation revealed the power of the situation to influence people's behaviour. Guards, prisoners, and researchers all conformed to their social roles within the prison.

  The more the guards identified with their roles, the more brutal and aggressive their behaviour became.
• A strength of the SPE is that the researchers had some control over variables.


  Emotionally stable participants were recruited and randomly assigned the roles of guard or prisoner. The guards and prisoners had those roles by chance. So their behaviour was due to the pressures of the situation and not their personalities. Control increases the study's internal validity. We can be more confident in drawing conclusions about the influences of social roles on behaviour.
• A potential limitation with the SPE is a lack of realism.


  Banuazizi suggests participants were play-acting. Their performances reflected stereotypes of how prisoners and guards are supposed to behave. One guard based his role on a character from a film. Prisoners also rioted because they thought that's what real prisoners did. But Zimbardo's data showed that 90% of the prisoners' conversations were about prison life. The simulation seemed real to them, increasing the study's internal validity.
• A limitation is that there were major ethical issues with the SPE. 


  One issue arose because Zimbardo was both lead researcher and prison superintendent. A student who wanted to leave the study spoke to Zimbardo , who responded as a superintendent worried about the running of his prison rather than as a researcher. This limited Zimbardo's ability to protect his participants from harm because his two roles conflicted with each other.