Confidence judgments in studies of individual differences

This paper examines psychometric properties of scores derived from calibration curves (overconfidence, calibration, resolution, and slope) and an analogue of overconfidence that is based on a posttest estimate of the proportion of correctly solved items. Four tests from the theory of fluid and crystallized intelligence were used, and two of these tests employed both sequential and simultaneous methods of item presentation. The results indicate that the overconfidence score not only has the highest reliability, but is the only score with a reliability normally considered adequate for use in individual differences research. There is some, albeit weak, difference in subjects' level of overconfidence between sequential and simultaneous methods of item presentation. Correlational evidence confirms our previous findings that overconfidence scores from perceptual and ‘knowledge’ tasks define the same factor. In agreement with the results of Gigerenzer, Hoffrage and Kleinbolting (1991), subjects' post-test estimates of their performance showed lower levels of overconfidence than did the traditional measures based on subjects' confidence judgment responses to individual items. Also, after controlling for the actual test performances, the post-test performance estimates and average confidence ratings were only slightly positively correlated, suggesting that different psychological processes may underlie these two measures. Finally, our results suggest that average confidence over all items in the test may be a more useful measure in individual differences research than scores derived from calibration curves.