In my social science training, I encountered the term “the Hawthorne effect,” in which – in the context of a study – “the subjects may respond differently just because they are being studied” . (For example, imagine you’re involved in a study of a diet pill, and you change your eating habits just because you’re keeping track of your eating.) Yesterday I encountered the “John Henry effect,” and I wondered where these terms come from.
The Hawthorn effect comes from the Hawthorne Works, a factory complex in Cicero, Illinois, in which a series of studies were carried out on factory workers between 1924 and 1932. Researchers increased light intensity and found that worker productivity increased. Then they reduced light intensity and found that – again – worker productivity increased. The fact that both studies increased productivity suggested that the fact of being studied increased productivity, rather than the intensity of the lights .
The John Henry effect is when people in your control group views itself as being in competition with the treatment group and so changes its behavior. (If you watch The Office, think of when Dwight tried to beat the company website in sales.) This comes from the story of John Henry trying to lay railroad track faster than the machine.
 See Source 1