Effects of prior destructive behavior, anonymity, and group presence on deindividuation and aggression.

Three of Zimbardo's deindividuation input variables (group presence, anonymity, and arousal) were manipulated in laboratory experiment, and their effects on aggression and deindividuation were measured. Only arousal produced a significant increase in aggression (p less than .05), while group presence produced a significant decrease in aggression (p less than .01). Anonymity had no significant effect on subjects' aggressiveness. Deindividuation per se was measured on a postsession questionnaire that assessed subjects' memory for their own aggressive behavior, self-consciousness, concern for social evaluation, and memory for central and peripheral cues. Only arousal condition participants showed deindividuation changes, but a factor analysis revealed that the deindividuation changes did not comprise a unified factor. Also it did not appear that the internal changes caused aggressive behavior, since the correlation between the two was low.