The identifiable victim effect is the tendency of individuals to offer greater aid when a specific, identifiable person ("victim") is observed under hardship, as compared to a large, vaguely defined group with the same need.
The identifiable victim effect has two components. People are more inclined to help an identified victim than an unidentified one, and people are more inclined to help a single identified victim than a group of identified victims. Although helping an identified victim may be commendable, the identifiable victim effect is considered a cognitive bias. From a consequentialist point of view, the cognitive error is the failure to offer N times as much help to N unidentified victims.
The identifiable victim effect has a mirror image that is sometimes called the identifiable perpetrator effect. Research has shown that individuals are more inclined to mete out punishment, even at their own expense, when they are punishing a specific, identified perpetrator.