In 1993 two Harvard psychologists, Nalini Ambady and Robert Rosenthal, published a study called “Half a Minute.” Nine undergraduates watched three 10-second clips of each of 13 college teachers, “with the audio turned down completely.” They rated each teacher on traits such as “confident,” “competent,” “enthusiastic” and “professional.”
Their ratings predicted the evaluations the teachers’ own students gave at the end of the semester. In a later part of the study, even shorter clips still predicted the evaluations.