John M. Darley

John M. Darley (April 3, 1938 – August 31, 2018) was an American social psychologist and professor of psychology and public affairs at Princeton University. Darley is best known, in collaboration with Bibb Latané, for developing theories that aim to explain why people might not intervene (i.e. offer aid) at the scene of an emergency when others are present; this phenomenon is known as the bystander effect and the accompanying diffusion of responsibility effect. This work stemmed from the tragic case of Kitty Genovese, a New Yorker who was murdered in March 1964 while 38 people either witnessed or heard her struggling with the assailant. Darley also studied the effect of assessment on performance and proposed Darley's Law, which states that “The more any quantitative performance measure is used to determine an individual’s rewards, the more subject it will be to corruption pressures and the more it will distort the action and thought patterns of those it is intended to monitor.”