Proceedings of the Annual Meeting of the Cognitive Science Society

Our world is filled with statistical information: from dice rolls to lotteries, we often act based on our impressions of probability. Yet the human mind is not wired to reason about truly probabilistic events, often imposing structure on data or events where no such structure exists (as in ‘illusory correlations’). Here, we consider a case study in intuitive statistics: disjunctive events. For example, participants are asked to imagine a button that, when pressed, has a 1 in 100 chance of yielding a prize. They are told to imagine pressing that button 100 times. Across several paradigms, we show that people overestimate the probability of this disjunctive event — in stark contrast to classic demonstrations where people underestimate such probabilities (e.g., when iteratively selecting marbles from jars with replacement). These results reflect a tendency to view events as causally connected in illusory ways; implications for other domains of reasoning are discussed.