Hawthorne effect
The idea that people change their behaviour because they know they're being observed or studied, so a study may measure the watching rather than the thing it tests.
In plain English
It's named after lighting experiments at a factory near Chicago in the 1920s, where output supposedly rose with every change, even dimming the lights. When the original data were finally analysed, that pattern wasn't there: untouched rooms improved too, dips matched the summer and Monday jumps happened every Monday. People can behave differently when watched, but the size of the effect varies a lot, and the safest defence is the same as always: a comparison group that is watched just as closely.
Uncle Gary explains
HR repainted the third floor and output rose from December to March. It rose from December to March last year too, with the old paint. HR called both of them a Hawthorne effect.
Why it matters for your money
Any before-and-after story about a new strategy, app or habit also measures the season, the market and the attention. Ask what happened over the same period to a group that didn't change anything.
Where we tested it
Related terms
All glossary terms. Educational content, not financial advice.