10.1177/0146167205284007PERSONALITY AND SOCIAL PSYCHOLOGY BULLETINEpley, Dunning / SELF-PREDICTION The Mixed Blessings of Self-Knowledge in Behavioral Prediction: Enhanced Discrimination but Exacerbated Bias

Four experiments demonstrate that self-knowledge provides a mixed blessing in behavioral prediction, depending on how accuracy is measured. Compared with predictions of others, self-knowledge tends to decrease overall accuracy by increasing bias (the mean difference between predicted behavior and reality) but tends to increase overall accuracy by also enhancing discrimina-tion (the correlation between predicted behavior and reality). Overall, participants ’ self-predictions overestimated the likeli-hood that they would engage in desirable behaviors (bias), whereas peer predictions were relatively unbiased. However, self-predictions also were more strongly correlated with individual differences in actual behavior (discrimination) than were peer predictions. Discussion addresses the costs and benefits of self-knowledge in behavioral prediction and the broader implica-tions of measuring judgmental accuracy of judgment in terms of bias versus discrimination