Teaching evaluations

How long, for example, did it take you, when you were in college, to decide how good a teacher your professor was? A class? Two classes? A semester? The psychologist Nalini Ambady once gave students three ten-second videotapes of a teacher - with the sound turned off - and they found they had no difficulty at all coming up with a rating of the teacher's effectiveness. Then Ambady cut the clips back to five seconds, and the ratings were the same. They were remarkably consistent even when she showed the students just two seconds of videotape. Then Ambady compared those snap judgments of teacher effectiveness with evaluations of those same professors made by their students after a full semester of classes, and she found that they were also essentially the same. A person watching a silent two-second video clip of a teacher he or she has never met will reach conclusions about how good that teacher is that are very similar to those for an entire semester. That's the power of our adaptive unconscious.

Malcolm Gladwell, Blink: The Power of Thinking Without Thinking, p. 12/13