Probative Inference from Phenomenal Coincidence: Demystifying the Doctrine of Chances

Abstract

The doctrine of chances remains a divisive rule in the law of evidence. Proponents of the doctrine argue that evidence of multiple unlikely events of a similar nature supports an objective, statistical inference of lack of accident or random chance on a particular occasion. Opponents argue that admissibility is improper because the underlying inference ultimately requires a forbidden form of character or propensity reasoning. Using formal probability modeling and simple numerical examples, this paper shows that neither side is correct. Contrary to the claims of its proponents, the doctrine of chances provides no novel or independent theory of relevance. But contrary to the claims of its opponents, the doctrine-of-chances inference does not require character or propensity reasoning. An intuitive way to understand these properties is to interpret the doctrine-of-chances inference as a weak form of any inference that could be permissibly drawn if extrinsic events were simply bad acts for which culpability or intent were certain.