When Blood Is Their Argument: Probabilities in Criminal Cases, Genetic Markers, and, Once Again, Bayes\u27 Theorem

Revolutionary advances in blood typing soon will cause a dramatic increase in the presentation of statistical evidence in criminal trials. Courts have admitted statistics into criminal trials before, and the proper use of this type of evidence has been debated previously. Until now, however, such mathematical evidence has been rare. Recently, however, a number of courts have admitted probability evidence derived from new and complex blood tests. Such evidence may soon be as commonplace as fingerprint testimony. The courts that have admitted this evidence, however, have done so without learning from past discussions about the proper role of statistical evidence. Because our criminal justice system is now at the threshold of an explosion in the presentation of this mathematical testimony, it is important to explore the use and misuse of such statistics in criminal trials. After surveying the recent and ongoing revolution in forensic serology, this article addresses the proper function of serological probability evidence at trial. The article examines, and rejects, recent commentary suggesting Bayes\u27 Theorem as a possible vehicle for presenting this statistical evidence at trial. The article concludes that at present no workable method exists for the effective and fair introduction of blood marker probability statistics at trial