PRAGMATIC ASPECTS OF THE BASE-RATE FALLACY

An investigation was made of the role played by verbal structure in th e problems used to study the base-rate fallacy, which has traditionall y been attributed to the role of heuristics (e.g. causality, specifici ty). It was hypothesized that elements of the verbal form of text prob lems led to a misunderstanding of the question or the specific informa tion, rendering obscure the independence of the sets of data (specific information is obtained independently from the base rate). Nine texts were presented to various groups of subjects: four were taken from Tv ersky and Kahneman (1980) and used as controls; five were obtained by modifying the verbal form of the original in order to reveal or concea l the links between the sets of data. The percentage of base-rate fall acies was greatly reduced with texts in which the independence of the data was clear, regardless of the causality and specificity of the inf ormation they contained (which was not changed). This result suggests that there is a need to consider the rules of natural language in orde r to move towards a better understanding of observed phenomena.