-contradictory findings - Reicher and Haslam - replicated zimbardo and participants didn't conform automatically
-individual differences control extent to which a person conforms to social roles. Zimbardos guards behaviour varied from sadistic to offering support
-breaking ethical guidelines - protection from harm, 5 left early, zimbardo acknowledged that it should of been stopped sooner
-only male participation - beta bias
+ initial real world application to improve prison system