Are Juries Competent to Evaluate Statistical Evidence

The issue of jury competence has arisen due to concerns about the ability of jurors to deal appropriately with the increasing complexity of evidence presented in trials. While most attention has focused on complex civil litigation,' criminal trials have grown more complex as well, due in part to revolutionary advances in the forensic sciences.2 New procedures for criminal identification, such as protein gel electrophoresis, DNA typing, gas chromotography, and neutron activation analysis have recently become available for use at trial.3 Additionally, the technology behind many of the more traditional identification techniques, such as bite mark comparison and hair comparison, has advanced in recent years.4 For a juror to understand and evaluate the technology underlying these techniques is often a formidable task in itself. Adding further to the difficulty is the probabilistic nature of much of this new evidence. The results of forensic tests are often meaningful only if they are accompanied by statistical data. For example, evidence that the defendant in a rape case has genetic markers matching those in semen recovered from a rape victim cannot be evaluated without statistical information on the frequency of the matching markers in the population. Because forensic tests are often less than perfectly reliable, statistical data on the error rate of the test may be necessary as well. 5 Hence, jurors may hear that a criminalist compared a sample of the defendant's blood to a semen sample taken from the rape victim using a procedure known as protein gel electrophoresis and found that the two samples contain a common set of genetic markers that collectively occur in only 1.5 percent of the population. The jurors may also hear, however, that proficiency tests have found that criminalists misclassify