Context affects the interpretation of low but not high numerical probabilities: A hypothesis testing account of subjective probability

Low numerical probabilities tend to be directionally ambiguous, meaning they can be interpreted either positively, suggesting the occurrence of the target event, or negatively, suggesting its non-occurrence. High numerical probabilities, however, are typically interpreted positively. We argue that the greater directional ambiguity of low numerical probabilities may make them more susceptible than high probabilities to contextual influences. Results from five experiments supported this premise, with perceived base rate affecting the interpretation of an event’s numerical posterior probability more when it was low than high. The effect is consistent with a confirmatory hypothesis testing process, with the relevant perceived base rate suggesting the directional hypothesis which people then test in a confirmatory manner.

► Lower numerical probabilities are directionally more ambiguous. ► This renders their interpretation more susceptible to contextual influences. ► We show that base rate affects subjective probability of lower probabilities more. ► A biased hypothesis testing process appears to underlie the proposed interaction. ► Potentially inappropriate base rate use contrasts with prevalent base-rate neglect.