Hawthorne effect
Also known as: Observer effect
People change their behavior simply because they know they're being observed.
What it means
The Hawthorne effect is the tendency for individuals to alter their behavior in response to the awareness of being observed or studied, rather than in response to the experimental manipulation itself. The mechanism is reactivity: knowing one is being watched and that one's performance matters heightens attention, effort, and motivation, so the act of measurement contaminates the very behavior it intends to measure. Its danger in research is that it can masquerade as a genuine treatment effect whenever a study lacks an adequate control group that experiences the same observation without the intervention. The effect is named after the Western Electric Hawthorne studies, in which worker productivity seemed to rise with almost any change to working conditions — but the historical case is now heavily questioned: re-analyses of the original data found the evidence weak and confounded, so the eponymous studies provide a shakier foundation than the widely repeated story implies. It matters nonetheless because reactivity to observation is a real and pervasive threat to validity, which is why blinding, unobtrusive measurement, and control conditions that hold observation constant are standard safeguards.
Examples
Asked to keep a food diary for a study, people eat more carefully than usual precisely because they know their eating is being recorded and watched.
Staff wash their hands far more often while an auditor is visibly on the ward, so the audit ends up measuring the audit as much as the routine it means to record.
A driving-test candidate checks mirrors constantly and stays under the limit, then reverts once the examiner is out of the car — the presence, not new skill, produced the performance.
First described in Western Electric Hawthorne studies (1920s–30s).