Evidence and Uncertainty in Subjective Prediction: Influences on Optimistic Judgment

Abstract

40 subjects were required to predict the future academic performance of 62 hypothetical students. Each student's performance was represented as a unique arrangement of above average and below average performance for 2, 3, 4, or 5 successively preceding semesters. Following each prediction, subjects were asked to rate how confident they were in their prediction. High confidence was associated with sequences of performance having lower uncertainty, but overestimation of future performance was associated with sequences having high uncertainty. The results were interpreted as supporting a conclusion that there is a positive bias in retrieving similar instances of evidence from memory to bear upon a decision and that the exclusion or reduction of available negative evidence leads to overestimation of future outcomes.