Polymorphism of Human Judgment under Uncertainty

The aim of this paper is to test if conjunctive and disjunctive judgments are differently accounted for possibility and probability theories depending on whether (1) judgments are made on a verbal or a numerical scale, (2) the plausibility of elementary hypotheses is low or high. 72 subjects had to rate the extent to which they believe that two characters were individually, in conjunction or in disjunction, involved in a police case. Scenarios differed on the plausibility of the elementary hypotheses. Results show that the possibilistic model tends to fit the subjects’ judgments in the low plausibility case, and the probabilistic model in the high plausibility case. Whatever the kind of scale, the possibilistic model matches the subjects’ judgments for disjunction, but only tends to do it for conjunction with a verbal scale. The probabilistic model fits the subjects’ judgments with a numerical scale, but only for disjunction. These results exhibit the polymorphism of human judgment under uncertainty.