Bin Miao

We study whether conjunction fallacies vary systematically with whether their constituent events are congruent in desirability. In an experiment conducted two days before the 2024 U.S. presidential election, participants evaluate lotteries contingent on electoral outcomes, economic outcomes, and their conjunctions, and report likelihood judgments for the same events. Political identity makes the desirability of electoral outcomes participant-specific, so that the same political-economic conjunction can be congruent for one participant and incongruent for another. We find conjunction fallacies in both beliefs and choices, and they are more pronounced when the constituent outcomes are either both favorable or both unfavorable. This pattern is robust to constituent order and disappears when the economic dimension has no natural desirability ordering. On the choice side, a conjunction fallacy violates statewise dominance. We develop an event-valence framework in which willingness to bet combines a component that is monotone in event inclusion with additive signed valence across states. We derive necessary and sufficient ordinal tests for the model and find that its predicted valence restrictions fit the data better than their sign-reversed counterparts.