The Hawthorne Effect: the proposition that workers are more motivated more by emotional than economic factors (i.e., by being involved and feeling important, rather than by an improvement in workplace conditions).
So called after workplace behavioral research by Elton Mayo at the Western Electric Company's Hawthorne plant in Cicero, Chicago, 1927-32, which ran on without Mayo until 1937. Mayo was a founding father of industrial psychology, attached to Harvard University as professor of industrial research from 1926, laying the foundations for later gurus, notably Herzberg (Motivation and Hygiene Factors), Maslow (Hierarchy of Needs), McGregor (XY Theory), Peters and Waterman ('In Search of Excellence' etc).
At a peak, 20,000 Western Electric employees were subject to research by a team of Harvard scientists and up to 100 investigators. This massive ten year programme grew from the initial experiment in which improved lighting was installed to assess the effect on workers' motivation and productivity. Sure enough, productivity increased, but productivity also increased in the 'control group' of workers where conditions were unchanged, except that they were informed they were part of the study.
This was perhaps the earliest significant demonstration that people are not actually motivated by improving their workplace conditions ('Taylorism' - after FW Taylor - had been the common view, in which money and conditions were thought to be the prime motivators). The Hawthorne Effect, and the experiments at the Hawthorne plant, proved that people are mainly motivated not by economic factors, but emotional factors, such as feeling involved and receiving attention.