Most people thing they are pretty good at reading people. But, how good are we really? When I am talking to students during my talks, I always tell them they were not created in the 90’s (Or whatever age group I am talking to). They were created thousands and thousands of years ago and these thin slicing skills I speak about have been handed down over time.

My favorite study about thin slicing is from the famous Ambady and Rosenthal study.

 A 1993 study by Nalini Ambady and Robert Rosenthal found just the opposite: students actually need much less information to make judgements that accurately predict end-of-semester evaluations.

Ambady and Rosenthal extracted 3, 10-second video clips of 13 teachers from tapes of entire class sessions. These 39 clips were randomized and presented without sound to 9 female college students, who rated them on a scale from 1 to 9 for a variety of behaviors, including “attentive,” “confident,” and “supportive.” The ratings were highly consistent between judges, with a global reliability measure of .85 overall.

 These teachers were rated by their own students at the end of the term on a general effectiveness scale. I’ve created a table below to show the correlation of the ratings of the 30 seconds’ worth of clips with the end-of-semester rating:

Accepting .50
Active .77
Attentive .48
Competent .56
Confident .82
Dominant .79
Empathetic .45
Enthusiastic .76
Honest .32
Likable .73
(Not) anxious .26
Optimistic .84
Professional .53
Supportive .55
Warm .67

The significant correlations — 9 of the 15 measures — are in boldface type. Concerned that their measure may only reflect a cursory evaluation of the physical attractiveness of the teachers, Ambady and Rosenthal had separate judges rate the teachers for attractiveness based on still photos. Even after controlling for physical attractiveness, the correlation between student ratings and the video clip ratings was still significant. Apparently after seeing just 30 seconds of nonverbal behavior, we can reliably predict teaching ability.

Not satisfied with comparing results only to student evaluations, Ambady and Rosenthal repeated the experiment with videotapes of high school teachers, and compared them to effectiveness ratings provided by the school principal. The results were comparable.

So how thin a slice of behavior is needed to accurately predict teaching ability? The researchers had an assistant unfamiliar with the task randomly select 5- and 2-second clips from the original 10-second clips. They repeated the rating task with a new group of female college students. The ratings for these shorter clips were less reliably correlated with the teacher effectiveness ratings, but amazingly, the 2-second ratings for college teachers were still significantly correlated with overall end-of-semester effectiveness ratings. Though these were the only short clips that were significantly correlated with effectiveness, neither the 5-second or 2-second ratings were significantly different from the 10-second ratings. What’s more, if the short ratings for college and high school teachers are combined, they do significantly predict effectiveness ratings.

So we do appear to be quite effective at making judgements about teaching ability even after viewing only a total of 6 seconds of actual teaching, and without even hearing the teacher’s voice.