What facilitates Bayesian reasoning? A crucial test of ecological rationality versus nested sets hypotheses.

Different theoretical views about Bayesian reasoning (ecological rationality and nested sets views) both claim support from results showing that natural sampling, whole numbers, and pictorial representations help with reasoning performance, although they differ in explaining how those results occur. Three studies (total N = 653) use minimally different numerical presentation formats-varying the singular or plural tense of the context story topic-and presence or absence of an additional icon array picture, to better understand the mechanisms driving these reasoning performance results. Plural wording, indicating a conceptual aggregation (i.e., frequencies) rather than just numerical whole numbers, consistently boosted performance. Icon arrays, in contrast, were helpful only when alongside single-tense information. These results fit more consistently with an ecological rationality view which has long argued that the mind is adapted to work best with frequentist information.