When many events contributed to an outcome, people consistently judge some more causal than others, basedin part on the prior probabilities of those events. For instance, when a tree bursts into flames, people judgethe lightning strike more of a cause than the presence of oxygen in the air – in part because oxygen is socommon, and lightning strikes are so rare. These effects, which play a major role in several prominent theoriesof token causation, have largely been studied through qualitative manipulations of the prior probabilities.Yet, there is good reason to think that people’s causal judgments are on a continuum – and relatively little isknown about how these judgments vary quantitatively as the prior probabilities change. In this paper, wemeasure people’s causal judgment across parametric manipulations of the prior probabilities of antecedentevents. Our experiments replicate previous qualitative findings, and also reveal several novel patterns thatare not well-described by existing theories.
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