“We now turn to the second type of problem, estimating a state. Here, only one person knows the answer and none of the problem solvers do. A classic example of this problem is asking a group to guess the number of jelly beans in a jar. We have been doing this experiment for over a decade at Columbia Business School, and the collective answer has proven remarkably accurate in most trials....
“Our 2007 jelly bean results illustrate the point. The average guess of the class was 1,151 while the actual number of beans was 1,116, a 3.1 percent error. Of the 73 estimates, only two were better than the average… There’s nothing unique about 2007; the results are the same year after year.”
Here’s a citation for my 2nd claim above about the accuracy of the mean:
www.leggmason.com/funds/knowledge/mauboussin/ExplainingWisdom.pdf
“We now turn to the second type of problem, estimating a state. Here, only one person knows the answer and none of the problem solvers do. A classic example of this problem is asking a group to guess the number of jelly beans in a jar. We have been doing this experiment for over a decade at Columbia Business School, and the collective answer has proven remarkably accurate in most trials....
“Our 2007 jelly bean results illustrate the point. The average guess of the class was 1,151 while the actual number of beans was 1,116, a 3.1 percent error. Of the 73 estimates, only two were better than the average… There’s nothing unique about 2007; the results are the same year after year.”