In 5 studies with overlapping designs and intents, Ss predicted a specific peer’s responses to a variety of stimulus situations, each of which offered a pair of mutually exclusive and exhaustive response alternatives. Each prediction was accompanied by a subjective probability estimate reflecting the Ss’ confidence in its accuracy—a measure validated in Study 5 by having Ss choose whether to “gamble” on the accuracy of their prediction or on the outcome of a simple aleatory event. In social prediction, as in other judgmental domains, Ss were highly overconfident. Regardless of the type of prediction item (e.g., responses to hypothetical dilemmas) and regardless of the type of information available about the person whose responses they were predicting (e.g., predictions about roommates), Ss’ accuracy levels fell below levels required to justify their confidence levels. Analysis revealed 2 sources of overconfidence. Ss generally were overconfident to the extent that they were highly confident. Also, Ss were most likely to be overconfident when they knowingly or unknowingly made predictions that ran counter to the relevant response base rates and, as a consequence, achieved low accuracy rates that their confidence estimates failed to anticipate.
Dunning, D., Griffin, D. W., Milojkovic, J. D., & Ross, L. (1990). The overconfidence effect in social prediction. Journal of Personality and Social Psychology, 58(4), 568-581.