Test difficulty and judgment bias

Two experiments tested the hypothesis that overconfidence in performance judgments is due to test- and person-driven errors. In Experiment 1, test difficulty accounted for the vast majority of variation in overconfidence when individuals judged items of varying difficulty within a homogeneous test. In Experiment 2, the severity of overconfidence did not differ between three unrelated tests once test difficulty was controlled. Both experiments supported the view that over-confidence is due largely to test difficulty. Some degree of overconfidence also occurred because individuals adopted a normatively high success criterion for judging their own test performance.