The Bystander Effect

Our Research


The bystander effect occurs when the presence of others discourages an individual from intervening or taking action.

The larger the group, the greater the probability of experiencing the bystander effect. The size of the group amplifies the bystander effect.

Explaining the Effect

Social psychologists credited with first describing the bystander effect, Latané and Darley attributed the bystander effect to:

  • perceived diffusion of responsibility (onlookers are more likely to intervene if there are few or no other witnesses) 
  • social influence (individuals in a group monitor the behavior of those around them to determine how to act). 


Social psychologists Latané and Darley popularized the concept following the infamous 1964 Kitty Genovese murder in NYC. Genovese was stabbed to death outside her apartment while bystanders who observed the crime did not step in to assist or call the police. 

In Genovese's case, each onlooker concluded from their neighbors' inaction that their own personal help was not needed.

A Video Explainer

Credit: Khan Academy 


[Content Warning: Details about violent crime around minute 4]

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