Can Jurors Understand Probabilistic Evidence?

Abstract

Some courts have been reluctant to admit testimony expressing probabilities because of a concern that jurors will overweight it relative to other evidence. However, empirical studies indicate a tendency to underweight statistical evidence when other sources of evidence are available. For more than two decades, researchers have studied the ways that people process probabilistic and statistical information, but only a small portion of these studies focuses on the capacity of jurors to process explicitly quantitative probabilistic evidence. This paper reviews this research. It concludes that the work has produced several insights into the factors that affect the judgments of mock jurors, and that it is valuable in devising optimal rules for the admission or exclusion of probability evidence. At the same time, we do not believe that the experiments published to date have been adequate in their design and implementation to demonstrate unequivocally the extent to which jurors attend to trace evidence or to identify what decision aids, if any, would promote an appropriate weighting of the evidence at trial.

Keywords: Probability, jurors, evidence