Comment: the doctrine of chances, brides of the bath and a reply to Sean Sullivan
The ‘Doctrine of Chances’ is a doctrine of probability that purports to solve an apparent logical conundrum or contradiction in the law of Evidence.
Sean P. Sullivan’s thought-provoking article, ‘Probative Inference from Phenomenal Coincidence: Demystifying the Doctrine of Chances’, is the latest scholarly attempt both to propound a sound probabilistic theory of calculating the odds and to demonstrate that the evidence can be offered in a way that does not involve propensity reasoning.
It is the authors' thesis in this article that the doctrine of chances—in any acceptable logical form including that described by Mr. Sullivan—does properly describe when this kind of ‘other wrongs’ evidence is relevant, and how probative it is, but that relevance and probative value where this kind of proof is offered does depend on propensity reasoning even under these theories even in the cases where they say it does not. He is not simply arguing that the jury will indulge propensity reasoning even though they are not supposed to and are instructed not to. Rather the author argues that propensity reasoning is a fundamentally necessary step in the inferential process they are told to perform.
However, it is also the authors' contention that it is not necessarily the type of propensity that the rule against propensity is meant to exclude. If properly understood, the rule and its exceptions will often admit the evidence when it is strong; will screen out only extremely prejudicial evidence or evidence of low probative value; and will do as satisfactory a job as is realistically possible in a large and diverse court system administered by probabilistically unsophisticated lawyers, judges and juries. In fact, it will produce results quite similar to what a more technically correct probabilistic approach, including Mr. Sullivan’s, would produce, particularly if a second step is applied after the relevance determination to screen out prejudicial evidence.