Diversity effects in subjective probability judgment

Previous research has shown that the judged probability of an event depends on whether its description mentions examples ("What is the probability that a randomly chosen Italian businessman will travel during the next month to Warsaw, Budapest, Prague or some other European city?") or does not mention examples ("What is the probability that a randomly chosen Italian businessman will travel during the next month to a European city?"). Here, we examined descriptions that mention examples and manipulated whether these are relatively similar (e.g., Warsaw, Budapest, Prague) or diverse (e.g., Warsaw, Marseilles, Helsinki). Four experiments (N = 1112) revealed a diversity effect: Overall, descriptions with diverse examples received higher probability judgments than descriptions with similar examples. We discuss several possible mechanisms for this effect, such as that descriptions with diverse examples prompt fuller representations of the target category or that the effect is driven by a representativeness or proximity heuristic.