DETERMINANTS OF NUMERICAL VERSUS VERBAL PROBABILITIES

The effects of various types of information upon numerical and verbal probability judgements were evaluated in six problems. Subjects judged the occurrence of a target event either by assessing the adequacy of the expressions probable and improbable or by assessing the numerical probability of the event. Different types of information were manipula ted for a given problem: the weight of the target in relation to the t otal weight of all alternatives (global weight) or in relation to that of each alternative independently (local weights), the change over ti me of the target's weight (trend), and the stated base rate. The resul ts revealed that particular types of information - for example local w eight - had different effects upon the two response modes. A tentative interpretation of this verbal-numerical discordance is proposed, sugg esting different strengths of use of the same information according to the response modes.