Proceedings of the Annual Meeting of the Cognitive Science Society

People make conjunction errors, rating a conjunction as morelikely than one of its constituents, across many different typesof problems. They commit the conjunction fallacy in problemsof social judgment, in physical reasoning tasks, and in gam-bles of pure chance. Doctors commit the fallacy when mak-ing judgments about hypothetical patients. Do all these errorsshare an underlying cause? Or does the fallacy arise indepen-dently in different types of reasoning? In a series of studies, welook for structure in conjunction errors across various types ofproblems. We find that error magnitudes are related for someclusters of items, but there does not appear to be a universalrelationship between all cases of this fallacy.