Information Acquisition and the Exclusion of Evidence in Trials

A peculiar principle of legal evidence in common law systems is that probative evidence may be excluded in order to increase the accuracy of fact-finding. A formal model is provided that rationalizes this principle. The key assumption is that the fact-finders (jurors) have a cognitive cost of processing evidence, an assumption well grounded in the psychological literature. Within this framework, the judge excludes evidence in order to incentivize the jury to focus on other, more probative evidence. Our analysis sheds light on two distinctive characteristics of this type of exclusionary rules. First, that broad exclusionary powers are delegated to the judge. Second, that exclusion by undue prejudice is peculiar to common law systems. Both features arise in our model.