Base rate evidence often connects a defendant to an act through the defendant’s membership in a certain population. It includes evidence arising from forensic analysis, criminal profiling, statistical analysis, artificial intelligence, and many other common and emerging scientific methods. But while this evidence is prevalent in civil and criminal trials, it is poorly understood, and there is little predictability in how a court will decide its admissibility or even what standard the court will apply.

In this Article, I show that although some forms of base rate evidence are desirable and even critical to achieving an accurate case outcome, a common form of base rate evidence called profile evidence often constitutes unrecognized character evidence—evidence that a defendant acted in accordance with a certain character trait—which is prohibited by federal and state evidentiary rules. To show this, and to describe precisely the relationship between base rate evidence and ordinary character evidence, I draw on a statistical tool called Bayesian inference to define a concept that I call predictive character evidence. Predictive character evidence describes a behavioral propensity of a population to suggest that an individual member of the population acted in accordance with this propensity. I show that this evidence—a form of base rate evidence that involves behavioral stereotyping—relies on character reasoning and is therefore impermissible under the rule against character evidence.

Finally, I discuss critical implications of my analysis. First, I show how an understanding of predictive character evidence helps resolve longstanding confusion and inconsistency surrounding base rate evidence and profile evidence in particular. I then demonstrate that applying the rule against character evidence to determine the admissibility of profile evidence is essential to achieving correct and predictable evidentiary decisions, to minimizing the influence of implicit biases based on race and other personal characteristics of a defendant, and to reaching accurate verdicts.