Who uses base rates and P(D/approximately H)? An analysis of individual differences.

In two experiments, involving over 900 subjects, we examined the cognitive correlates of the tendency to view P(D/approximately H) and base rate information as relevant to probability assessment. We found that individuals who viewed P(D/approximately H) as relevant in a selection task and who used it to make the proper Bayesian adjustment in a probability assessment task scored higher on tests of cognitive ability and were better deductive and inductive reasoners. They were less biased by prior beliefs and more data-driven on a covariation assessment task. In contrast, individuals who thought that base rates were relevant did not display better reasoning skill or higher cognitive ability. Our results parallel disputes about the normative status of various components of the Bayesian formula in interesting ways. It is argued that patterns of covariance among reasoning tasks may have implications for inferences about what individuals are trying to optimize in a rational analysis (J. R. Anderson, 1990, 1991).