The bystander effect occurs when the presence of others discourages an individual from intervening in an emergency situation. Social psychologists Bibb Latané and John Darley popularized the concept following the infamous 1964 Kitty Genovese murder in New York City. Genovese was stabbed to death outside her apartment while bystanders who observed the crime did not step in to assist or call the police. Latané and Darley attributed the bystander effect to the perceived diffusion of responsibility (onlookers are more likely to intervene if there are few or no other witnesses) and social influence (individuals in a group monitor the behavior of those around them to determine how to act). In Genovese's case, each onlooker concluded from their neighbors' inaction that their own personal help was not needed.