This research note reports on two studies run to determine whether the interpretations of statements, or forecasts, using vague probability and frequency expressions such as "likely", "improbable","frequently", "rarely" were sensitive to the base rates of the events involved. In the first experiment, professional weather forucasters judged situations drawn from a medical context. In the second, students judged matched forecast scenarios of common semantic content that differed only in prior probability (as determined by an independent group of subjects). Results were as follows: the interpretations of forecasts using neutral terms (e.g. possible) and terms above neutral (e.g. usually) were strong, positive functions of base rate, while the interpretations of forecasts using terms below neutral (e.g. rarely) were much less affected by base rates; in the second experiment, interpretations of forecasts appeared to represent some kind of average of the meaning of the expression and the base rate
