Observer effect
Not a bias
The fact that observing something can change it. In everyday life, people often act differently when they know they are being watched, so what we observe may not reflect normal behavior. It is a measurement problem more than a bias, and it misleads us when we forget to account for it; a closely related idea is the Hawthorne effect.
In everyday life
Nurses wash their hands more often while an inspector is on the ward, so the audit shows better hygiene than on a normal day.
The week new security cameras go up in the office, everyone arrives on time, and the manager concludes the team has always been punctual.
Why your mind does this
Holding steady beliefs lets us act without rethinking everything each time. Favoring information that fits what we already know is fast, protects our sense of being right, and keeps our picture of the world stable and coherent.
Its family, in 30 seconds: Confirms beliefs
How to spot it
Ask yourself whether the people or system you are measuring know they are being measured.
What you can do
Collect data over longer periods or in less noticeable ways, so people settle back into their usual habits.
Same family: Confirms beliefs
SourcesSrigley et al. (2014)·Wikipedia