A model for realism of confidence judgments: implications for underconfidence in sensory discrimination

In a recent issue of this journal, Björkman, Justlin, and Winman (1993) presented a model of the calibration of subjective confidence judgments for sensory discrimination which they called "subjective distance theory." They proposed that there was a robust underconfidence bias in such judgments, that the model predicted such a bias, and that two different models were needed for the calibration of subjective confidence for cognitive judgments and for sensory ones. This paper addresses issues they raised. It points out that they have not presented a new model, but rather a portion of a more general one, the "decision-variable partition model" originally proposed in Ferrell and McGoey (1980). This paper explores properties of the model and shows, contrary to Björkman, Juslin, and Winman's hypotheses, that the model does not predict underconfidence, that the "hard-easy effect" can be observed with sensory discriminations, and that the model fits not only sensory, but also cognitive judgments.