Trial by Numbers

Abstract

Legal cases often require jurors to use numerical information. They may need to evaluate the meaning of specific numbers, such as the probability of match between a suspect and a DNA sample, or they may need to arrive at a sound numerical judgment, such as a money damage award. Thus, it is important to know how jurors understand numerical information, and what steps can be taken to increase juror comprehension and appropriate application of numerical evidence. In this Article, we examine two types of juror decisions involving numbers––decisions in which jurors must convert numbers into meaning (such as by understanding numerical evidence in order to determine guilt or liability), and decisions in which jurors must convert meaning into numbers (such as by understanding qualitative evidence and converting this into a numerical damage award amount). In each of these areas we analyze legal cases and research to examine areas in which dealing with numbers leads to sound or sub-optimal decision making in jurors. We then examine psychological theory and research on numerical decision making to understand how informed, fair, and consistent juror decision making about numbers can be promoted. We conclude that what is often most important is juror understanding of the meaning of numbers in context rather than technically precise numerical ability, supporting the role of the lay jury. We also suggest how to improve juror understanding, so that jury decisions better reflect considered community judgment.