This wonderful profile of documentary filmmaker Frederick Wiseman confirms my own experience with this frequently-asked-question about user research.

“There’s a whole issue as to whether the camera changes behavior — the pretentious way of talking about it is, ‘Does the Heisenberg principle apply to documentary filmmaking?’ — but in my experience, 99.9 percent of the people don’t act for the camera,” he said. “My explanation for that is most people aren’t good enough actors to become somebody else. Not everybody’s Meryl Streep. And when people are uncomfortable or putting it on, so to speak, you instantly know it.”