Biases in thinking
Hawthorne effect
Also called Observer effect
People change their behaviour when they know they're being watched, which can skew what research observes.
Participants in a usability test try harder, persist longer and are more polite than they would be alone. Employees in a study work differently while it lasts.
Reduce it with realistic tasks, reassurance that you're testing the product rather than them, and data from real use, such as analytics, alongside what you observe.
In practice
In a moderated test, a participant keeps going through a confusing form they would have abandoned at home.
Common mistake
Treating lab results as real-world numbers. Completion rates in a study are usually higher than in the wild.
Where it comes from
Named by Henry Landsberger in 1958 after studies at Western Electric's Hawthorne Works in the 1920s and 1930s. Later reanalysis of the original data found little evidence for the effect as first told.