The Hawthorne effect is a type of reactivity in which individuals modify an aspect of their behavior in response to their awareness of being observed. The effect was discovered in the context of research conducted at the Hawthorne Western Electric plant; however, some scholars feel the descriptions are apocryphal.

The original research involved workers who made electrical relays at the Hawthorne Works, a Western Electric plant in Cicero, Illinois. Between 1924 and 1927, the lighting study was conducted. Workers experienced a series of lighting changes in which productivity was said to increase with almost any change in the lighting. This turned out not to be true. In the study that was associated with Elton Mayo, which ran from 1928 to 1932, a series of changes in work structure were implemented (e.g., changes in rest periods) in a group of five women. However, this was a methodologically poor, uncontrolled study that did not permit any firm conclusions to be drawn.

One of the later interpretations by Landsberger suggested that the novelty of being research subjects and the increased attention from such could lead to temporary increases in workers' productivity. This interpretation was dubbed "the Hawthorne effect".