Tech & Science dictionary

bystander effect

[ bahy-stan-der ih-fekt ]

What is the bystander effect?

The bystander effect is a phenomenon in which an individual person is less likely to intervene or assist in an emergency, crisis, or altercation that they are witnessing due to the presence of other people also witnessing it.

For example: When a person is struck by a car in front of multiple witnesses, individuals in the crowd may not (or may not initially) check on the victim or call for help. The inaction of these witnesses is often attributed to the bystander effect. Though many factors may be involved, it is often thought to be due to each person assuming that someone else will come forward to help—or each person preferring that someone else would.

According to research on the bystander effect, the likelihood of a person taking action in such a situation actually decreases in proportion to how many people are present. In contrast, it’s more likely for a single person to intervene when no one else is around.

Related words

Mandela Effect, CSI effect, Streisand effect

Where does bystander effect come from?

image of large group of people

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.

Examples of bystander effect

Experts have long studied how people react in dangerous or distressing public situations, often turning to a psychological theory known as the bystander effect to describe people who are less likely to help victims when they are in group settings.
Minyvonne Burke and Alicia Victoria Lozano, NBC News, October 2021
A humble plea to please, please always check on people you see passed out or otherwise incapacitated in public.  Even just a "Hey man, you doing okay?" from two metres away is better than nothing. Don't let the bystander effect cost someone their wellbeing or life.
@xjackiehong, October 21, 2021

Who uses bystander effect?

Use of the term bystander effect has become common among researchers studying the phenomenon as well as in news stories and discussion about such events.

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