Gary L. Wells and Donna M. Murray (1984), “Eyewitness
confidence,” in Gary L. Wells and E. F. Loftus, (eds), Eyewitness
Testimony: Psychological Perspectives, New York: Cambridge
Prior research has shown that an eyewitness's expressed confidence affects the extent to which people will believe in
that witness's testimony. Jurors show much agreement in assessing the certainty expressed by the witness. It is interesting, then, to find that eyewitness confidence has little predictive validity. Wells and Murray performed a meta-analysis on 31 previously published studies. The typical correlation between confidence and accuracy was only 0.07. This means that confidence explains less than 1 percent of the variance in accuracy. Wells explains this by saying that some variables affect accuracy of judgment whereas other variables affect confidence. This result fits into a pattern of studies showing that individual confidence ratings are poor guides to accuracy unless the feedback in the task is exceptionally good. This pattern has a practical implication: do not ask individuals how confident they are in their judgmental forecasts.