Forensic science is playing an increasingly important role in the justice system but it poses special challenges for lay jurors. To evaluate forensic evidence, jurors often must consider mathematical or statistical data, such as random match probabilities, false positive rates, and likelihood ratios. In order to learn more about jurors' ability to understand and use such data, a series of four jury-simulation experiments will be conducted at a county courthouse. As they are released from jury duty, jurors will be invited to remain in the jury assembly room to read and evaluate summaries of evidence in hypothetical cases. The nature of the forensic evidence, and the way it is presented, will be varied experimentally in order to test a series of hypotheses about jurors' use (and possible misuse) of forensic statistics. The goal of the research is to identify potential misunderstandings and inferential errors and find ways to correct them as well as learning which methods of presentation best promote clear understanding.
The proposed studies are more sophisticated than previous research in this area on several dimensions. First, they address realistic and important issues that frequently arise when forensic evidence is presented to juries. Second, they employ more sophisticated normative models than those used in previous studies as standards of comparison against which jurors' actual judgments can be evaluated. Third, they examine the judgments of a representative sample of citizens from an actual jury pool (rather than undergraduates). Finally, although these studies are primarily designed to answer practical questions of importance to the legal system, they are also informed by (and designed to address) broader theoretical issues in the psychology of human judgment and decision-making. They will extend and test the limits of existing theories of probabilistic judgment and, in particular, will explore people's susceptibility to several forms of fallacious reasoning when dealing with quantitative data.
Broader Impacts: In 1996, the National Research Council recommended that behavioral research be carried out "to identify any conditions that might cause a trier-of-fact to misinterpret evidence on DNA profiling and to assess how well various ways of presenting expert testimony on DNA can reduce any such misunderstandings" (NRC, 1996, Recommendation 6.1). Since that time, relatively few such behavioral studies have been published and the potential for misunderstanding DNA evidence, and other types of forensic evidence, remains an important concern. The studies proposed here take an important step toward addressing that concern. They examine a series of novel questions, never before addressed, that must be answered if we wish to know how (and how well) jurors understand forensic evidence. These studies will help identify circumstances in which jurors are likely to misinterpret forensic evidence, giving it more (or less) weight than it deserves. This knowledge will be helpful to courts in evaluating the admissibility of contested forensic evidence. It will also provide much needed guidance on presenting forensic evidence in a manner that is effective and fair. The broad theoretical framework of the research makes it relevant to a wide range of evidence in the forensic identification sciences.