Proceedings of the Annual Meeting of the Cognitive Science Society

Two experiments examined theoretical accounts of why people fail to consider alternative hypotheses in judgments under uncertainty. Experiment 1 found that a majority of participants failed to spontaneously search for information about an alternative hypothesis, even when this required minimal effort. This bias was reduced when a specific alternative was mentioned before search. Experiment 2 showed that when participants were given the likelihoods of the data given a focal hypothesis p(D|H) and an alternative hypothesis p(D|¬H), they gave estimates of p(H|D) that were consistent with Bayesian principles. The results show that neglect of the alternative hypothesis typically occurs at the initial stage of problem representation. However judgments are more consistent with Bayesian norms when they involve utilizing information about a given alternative