Proceedings of the Annual Meeting of the Cognitive Science Society

The disjunction effect (DE) refers to an empirical violation of the Sure-Thing Principle, which states that if a person is willing to take an action independently of the outcome of some event, then they must be willing to do so even when the outcome of the event is unknown. In practice, authors report a population-level version of this phenomenon, specifically that fewer people are willing to take the proposed action when the outcome of the event is unknown than for any possible known outcome. This latter condition has received a lot of attention, because it presumably violates the Law of Total Probability. Here we show that this assertion is false and, consequently, this population-level version cannot be interpreted as a DE. This calls for a reevaluation of experimental results that have been interpreted as showing a DE based on the above condition.