In the 1930s, the Hawthorne Plant, a factory for telephone parts outside of Chicago, commissioned a study to examine whether a change in shop-floor lighting would improve worker’s productivity. And indeed, when the lighting was made brighter, productivity increased. However, when the lighting was dimmed, productivity also increased! It did not matter what was changed: productivity always went up (for a short time). In general, people behave differently when they know they are being watched compared to when they do not—this phenomenon is now known as the Hawthorne effect.
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