Hawthorne effect – Φαινόμενο Hawthorne (see also “observer effect”)

The Hawthorne effect (also referred to as the observer effect) is a type of reactivity in which individuals modify or improve an aspect of their behavior in response to their awareness of being observed.

It is the tendency for people to improve their performance after any change when they know their performance is being studied — a common potential confound when testing user interface changes for whether they represent an improvement or not.