Choice Set Size Neglect in Predicting Others' Preferences

An inherent feature of any choice is the set size from which that choice is made (i.e., the number of available options in a choice set). Choice set size impacts the likelihood of landing on a more preferred option: Larger sets are more likely to contain an option matching one's preferences. Nevertheless, in six preregistered experiments with 10,092 U.S. adults, we demonstrated that people consistently underestimated the effect of set size when predicting others' liking for a chosen option. We propose this effect arises because, although people recognize that set size predicts liking of a chosen option, they typically fail to attend to it when considering others' choices. Accordingly, this effect was attenuated when attention was drawn to set size, specifically (a) when participants considered multiple set sizes simultaneously, (b) when the decision process was framed as ranking rather than choosing, or (c) when participants were prompted to recall set size before predicting others' preferences.