Why is “Quite Certain” More Informative than “Slight Possibility”? Information Theoretic Analysis of the Informativeness of Probability Statements

This research aims to establish a quantitative relation between probability statements and their “informativeness.” Keren & Teigen (2001) proposed the “search for definitive predictions” principle. According to this principle, relatively high or low probabilities are preferred to medium ones because high or low probabilities denote the occurrence or nonoccurrence of a single outcome more strongly than they do medium ones. This research formalizes the judgment of the informativeness of probability statements in terms of the information theory and argues that the search for definitive predictions principle can be interpreted as rational information estimation under the rarity assumption (Oaksford & Chater, 1994). The results of two empirical studies supported this argument.