The vagueness and the directionality of verbal probability expressions

The properties of probability information and their effects on decision making

Abstract

We examined the relationship between two properties of verbal probability (VP) expressions, “vagueness” and “directionality”, and investigated the effects of these properties on decision making. Vagueness is defined as its imprecise characteristic of uncertainty expressions in VP, whereas the directionality is communicative functions which cause one to focus on the occurrence or non-occurrence of the target event described by VP. Experiment 1 contrasted a disagreement in the literature as to whether one can predict the directionality from vagueness properties, and our analyses resolved the conflict by showing the ineffectiveness of the vagueness in predicting the directionality. Experiment 2 administered decision tasks involving VP and numerical translation tasks of VP. We discovered that the directionality affects only on decision tasks. The results of Experiments 1 and 2 indicated that the directionality is distinct characteristic from the vagueness of VP, and these properties affect decisions independently. Implications are discussed.