Document Type


Publication Date

Fall 11-13-1997


Representational accounts for errors in reasoning about conjunctions and disjunctions of events were contrasted with accounts based on the algebraic combination of simple event likelihoods. In a series of two experiments, patterns in judgments about complex events were explored when the differing strategies were likely to be used. Evidence was gathered to determine when representations of complex events are likely to be constructed, and how judgments about complex events are derived when a representation is available. A particular representational account of judgment and decision making, explanation-based decision making, is explored as an account for errors in reasoning about conjunctions and disjunctions of events. As predicted, likelihood judgments for conjunctions of explanations consistently were above the estimated likelihoods of at least one of the component explanations, and likelihood judgments for disjunctions of explanations consistently fell below likelihoods of the more likely component explanations for common scenario problems. Furthermore, conjunction judgments were found to depend on the relationship between component explanations, a finding predicted by explanation-based decision making and consistent only with representational accounts of reasoning. However, disjunction judgments were not sensitive to the relationship between component explanations, suggesting that subjects may invoke a calculational strategy when assessing some types of disjunctive events. The findings of this research provide support for both representational and calculational accounts, and suggest that the representation of events plays in important role in the selection of strategies that are used to solve judgment problems.