Timothy Hart and Ternace Miethe used data from the National Crime Victimization Survey (NCVS) and found that a bystander was present in 65 percent of the violent victimizations in the data. Their presence was most common in cases of physical assaults (68%), which accounted for the majority of these violent victimizations and less likely in robberies (49%) and sexual assaults (28%). The actions of bystanders were most frequently judged by victims as “neither helping nor hurting” (48%), followed by “helping” (37%), “hurting” (10%), and “both helping and hurting” (3%). Half of the attacks that a bystander was present at occurred in the evening and the victim and bystander were strangers.


There are, in fact, many reasons why bystanders in groups fail to act in emergency situations, but social psychologists have focused most of their attention on two major factors. According to a basic principle of social influence, bystanders monitor the reactions of other people in an emergency situation to see if others think that it is necessary to intervene. Since everyone is doing exactly the same thing (nothing), they all conclude from the inaction of others that help is not needed. This is an example of pluralistic ignorance or social proof. The other major obstacle to intervention is known as diffusion of responsibility. This occurs when observers all assume that someone else is going to intervene and so each individual feels less responsible and refrains from doing anything.

Source: http://en.wikipedia.org/wiki/Bystander_effect