Article

The Hawthorne Effect or Observer Bias in User Research

Nielsen Norman Group Free Intermediate

This explains why people behave differently the instant they know you're watching, which is the deeper reason your own presence in the room is already a source of bias before you say a single word. The mitigation tactics here (building rapport, giving people a real task instead of a demo, stepping back physically) are direct, practical fixes.

• Being watched changes behavior even if the observer never speaks.
• A real goal and enough time in the task reduce self-consciousness.
• Some observer effect is unavoidable; the goal is to shrink it, not eliminate it.