The Effects of Averaging Subjective Probability Estimates Between and Within Judges
Journal of Experimental Psychology: Applied, 6 (2):
130--147 (June 2000)DOI: 10.1037/1076-898X.6.2.130
Abstract
The average probability estimate of J > 1 judges is generally better than its components. Two studies test 3 predictions regarding averaging that follow from theorems based on a cognitive model of the judges and idealizations of the judgment situation. Prediction 1 is that the average of conditionally pairwise independent estimates will be highly diagnostic, and Prediction 2 is that the average of dependent estimates (differing only by independent error terms) may be well calibrated. Prediction 3 contrasts between- and within-subject averaging. Results demonstrate the predictions' robustness by showing the extent to which they hold as the information conditions depart from the ideal and as J increases. Practical consequences are that (a) substantial improvement can be obtained with as few as 2–6 judges and (b) the decision maker can estimate the nature of the expected improvement by considering the information conditions.