COMMENTS ON THE STATISTICAL ASPECTS OF THE NRCS REPORT ON DNA TYPING

The goal of the MIC report on DNA typing was to answer a ''crescendo o f questions concerning DNA typing,'' many of them in the areas of popu lation genetics and statistics. Unfortunately, few of these questions were answered adequately. In lieu of answering these questions, the pa nel proposed another conservative method of forensic inference, the '' ceiling principle.'' Aside from its extreme conservativeness, this new method is difficult to justify because it is based on inadequate popu lation genetics and statistical theory. Moreover, in its ultimate impl ementation, the panel's method will depend on a population genetics st udy whose rationale is questionable. In this article, we elaborate som e of the general comments we made about the NRC report in a recent art icle [1]. Specifically we cover three topics. First we question the st atistical basis for the ceiling principle, showing that the empirical results that motivated the method are likely to be misinterpreted and showing, by power calculations, that the effects of population substru cture cannot be substantial. Second, we show that the study design to determine ''ceiling'' allele frequencies has several undesirable stati stical properties. Finally, we discuss the estimation of handling erro rs from the statistical perspective, a subject treated inadequately by the report.