Zimbardo stanford prison experiment

• Zimbardo's research

  In the 1970s Philip Zimbardo and colleagues conducted one of the most memorable studies in psychology
• Purpose of the Stanford prison experiment (SPE)

  • To know why prison guards behave brutally - was it because they have sadistic personalities or was it their social role (as a prison guard) that created such behaviour?
• The Stanford prison experiment (SPE)

  1. Zimbardo et al. (1973) set up a mock prison in the basement of the psychology department at Stanford University

  2. They selected 21 men (student volunteers) who tested as 'emotionally stable'

  3. The students were randomly assigned to play the role of prison guard or prisoner

  4. Prisoners and guards were encouraged to conform to social roles both through the uniforms they wore and also instructions about their behaviour
• Uniforms


  • The prisoners were given a loose smock to wear and a cap to cover their hair, and they were identified by number (their names were never used)
  • The guards had their own uniform reflecting the status of their role, with wooden club, handcuffs and mirror shades
• De-individuation

  The uniforms created a loss of personal identity
• Instructions about behaviour


  1. Prisoners could 'apply for parole' rather than leaving the study early

  2. The guards were encouraged to play their role by being reminded that they had complete power over the prisoners
• Strengths of the SPE

  • Zimbardo and his colleagues had control over key variables
  • Emotionally-stable individuals were chosen and randomly assigned to the roles of guard and prisoner, ruling out individual personality differences as an explanation
• Limitations of the SPE

  • It did not have the realism of a true prison, participants were merely play-acting rather than genuinely conforming to a role
  • Zimbardo may have exaggerated the power of social roles to influence behaviour, only one-third of the guards actually behaved in a brutal manner