A number of studies have reported that there is a strong tendency to ignore base-rate information in favor of individuating information, except when the former can readily be incorporated into a causal schema. In this study, students in eight undergraduate classes were given problems in which the base-rate information was either causal or noncausal and either incongruent or congruent with the individuating information. In addition, 12 subjects were interviewed as they attempted to solve several versions of one of the problems. The results indicated: (1) strong individual differences in the perceived importance of base-rate information and even in how the probability estimation task itself was interpreted; and (2) greater use of base-rate information congruent with the individuating information than of base-rate information which is incongruent. The interview data indicate that it is difficult to determine from the answer alone whether or not the subject thought that the base-rate information was relevant. These data also suggest that subjects have different strategies for dealing with probability estimation problems. (Author/TW)