When does a response error become a judgmental bias? Commentary on "Judged Frequency of Lethal Events".

The study of Lichtenstein, Slovic, Fischhoff, Layman, and Combs reports several types of errors in subjects' frequency judgments of lethal events. These errors are interpreted as reflecting the operation of two types of judgment biases. In this research, the objective or actual frequency of lethal events served as a standard of comparison; any deviation from this standard was defined as a bias. Thus, the research strategy used is apparently modeled after that of a psychophysicist using illusions to study basic perceptual processes. There is one key difference, however. In the case of illusions, the subject is directly exposed to the physical stimulus object. In the present study, however, subjects were never exposed to actual stimuli. Since subjects were asked to make judgments about things they had not directly experienced, it is not surprising that they would be inaccurate. But unlike the study of illusions, such inaccuracies have not been shown to have any necessary connection to psychological mechanisms. Therefore, it seems somewhat tenuous to offer psychological interpretations of judgmental biases when the origins of those biases have not yet been identified.