bystander effect

The word bystander means “a person present but not involved; spectator; onlooker.” In other words, a bystander is sometimes who stands by but does not get involved or take action.

The word effect is often used in the names of psychological phenomena, such as the placebo effect and the Mandela effect.

Researchers Bibb Latane and John Darley popularized the concept of the bystander effect in the late 1960s. Latane and Darley conducted multiple experiments to study bystander inaction following the 1964 murder of Kitty Genovese, which drew widespread media attention due to reports that none of the at least 38 people who witnessed the incident attempted to intervene or call the police. Though these reports were later revealed to be inaccurate, the case became well-known and closely associated with the term bystander effect. The term itself has since become common among researchers as well as in popular discussion of such incidents.

Psychologically, the bystander effect is often attributed to people being influenced by the inaction of others around them, or to what psychologists call diffusion of responsibility, which refers to a phenomenon in which people feel less personal responsibility when there are more people around them.

It is mainly discussed in the context of emergencies and cases involving violent crime. For example, the bystander effect is commonly cited as a reason for bystander inaction during instances of sexual assault.