AVAILABILITY OF INFORMATION AND THE AGGREGATION OF CONFIDENCE IN PRIOR DECISIONS

Recent research on calibration has shown that judgments about aggregat e performance are consistently lower in magnitude than confidence-judg ments about single items (the ''aggregation effect''). Three explanati ons of this effect have been proposed: Probabilistic Mental Models the ory, the regression-to-the-mean hypothesis, and the dual-source hypoth esis. In two studies, we tested predictions based on these explanation s about the influence of availability of information on the aggregatio n effect. Study 1 showed that neither reducing the item set size for a ggregate-item judgments nor delaying the single-item judgments elimina ted the effect, Study 2 showed a persistent aggregation effect for dif ferent kinds of item lists and reminders. Further comparisons showed t hat discrimination (as distinguished from overconfidence) was (1) cons istently better for single-item judgments than for aggregate-item judg ments, and (2) improved when there is a delay between the choosing of an answer and the rating of confidence about that answer. The three pr oposed explanations of the aggregation effect are compared in light of these findings. (C) 1996 Academic Press, Inc.