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The bystander effect or bystander intervention (also known as bystander apathy) is a psychological phenomenon in which someone is less likely to intervene in an emergency situation when others are present than when they are alone.


Solitary individuals will typically intervene if another person is in need of help: this is known as bystander intervention. However, researchers were surprised to find that help is less likely to be given if more people are present. In some situations, a large group of bystanders may fail to help a person who obviously needs help. An example which shocked many people is the Kitty Genovese case. Kitty Genovese was stabbed to death in 1964 by a serial rapist and murderer. The murder took place over a period of about thirty minutes, during which dozens of alleged "witnesses" failed to help the victim. For this reason, the name Genovese syndrome or Genovese effect was used to describe the phenomenon at the time. The death of Deletha Word in 1995 after witnesses failed to thwart her attackers, as well as the James Bulger murder case, may have been other well-publicized cases of the effect.

A 1968 study by John Darley and Bibb Latane first demonstrated the bystander effect in the laboratory. They ran some simple studies such as the following: A subject is placed alone in a room and is told he can communicate with other subjects through an intercom. In reality, he is just listening to an audio recording and is told his microphone will be off until it is his turn to speak. During the recording, one subject suddenly pretends he is having a seizure. The study found that how long the subject waits before alerting the experimenter varies inversely with the number of other subjects. In some cases, the subject never told the experimenter.

The most common explanation of this phenomenon is that, with others present, observers all assume that someone else is going to intervene and so they each individually refrain from doing so. This is an example of how diffusion of responsibility leads to social loafing. People may also assume that other bystanders may be more qualified to help, such as being a doctor or police officer, and their intervention would thus be unneeded. People may also fear "losing face" in front of the other bystanders, being superseded by a "superior" helper, or offering unwanted assistance. Another explanation is that bystanders monitor the reactions of other people in an emergency situation to see if others think that it is necessary to intervene. Since others are doing exactly the same, everyone concludes from the inaction of others that other people do not think that help is needed. This is an example of pluralistic ignorance and social proof.

A victim may be able to counter the bystander effect by picking a specific person in the crowd to appeal to for help rather than appealing to the larger group generally. This places all responsibility on that specific person instead of allowing it to diffuse. Furthermore, pluralistic ignorance is countered by the implication that all bystanders are indeed interested in helping, and social proof kicks in when one or more of the crowd steps in to assist.

See also


  • Darley,J. M. & Latane,B. (1968). Bystander intervention in emergencies: Diffusion of responsibility. Journal of Personality and Social Psychology 8, 377-383.
  • Latane, B. and Darley, J.M. (1968) Group inhibition of bystander intervention in emergencies, Journal of Personality and Social Psychology 10: 215-21.
  • Latane, B. and Rodin,J.(1969) A lady in distress: inhibiting effects of friends and strangers on bystander intervention, Journal of Experimental Social Psychology 5(2): 189-202.
  • Gladwell, Malcolm. (2000). The Tipping Point: How Little Things Can Make a Big Difference. ISBN 0-316-31696-2.

External links

fr:Effet du témoin he:פיזור אחריות de:Bystander-Effekt