The disjunction effect reexamined: Relevant methodological issues and the fallacy of unspecified percentage comparisons

Leonard J. Savage’s sure-thing principle (1954) is a key assumption of the consequentialist conception of decision making under uncertainty, which more-or-less assumes that decision makers are rational and thorough. The sure-thing principle states that if some option x is preferred given some other event A occurs, and if option x is preferred given this event A does not occur, then x should be preferred even when the outcome of A is unknown. Tversky and Shafir [Tversky, A., &; Shafir, E. (1992). The disjunction effect in choice under uncertainty. Psychological Science, 3(5) 305–309] claim that this basic principle is frequently violated in two-step gambles. They call such violations disjunction effects. Kuhberber, Komunska, and Perner [Kuhberber, A., Komunska, D., &; Perner, J. (2001). The disjunction effect: does it exist for two step gambles? Organizational Behavior and Human Decision Processes, 85(2) 250–264] attempted to replicate Tversky and Shafir’s findings and claim their results show that people do not violate the sure-thing principle in repeated gambles. This article evaluates Kuhberger, Komunska, and Perner’s claims, suggesting they did not appropriately analyze their results, and further provides evidence that people do regularly violate the sure-thing principle in two-step gambles, providing further evidence for the reality of disjunction effects.