Statistical Inference from DNA Evidence

When a decision has to be made whether or not a given suspect has committed a crime, or is the father of a disowned child, critical information to assist decision making can be provided by genetics experts. Biological traces from crime scenes often contain sufficient amounts of DNA or protein to allow inferences to be made about the source genotype at a number of marker loci. In kinship testing, extensive use is made of the fact that genotypes show more resemblance between close relatives than between unrelated individuals. The task of the statistical geneticist then is to calculate, under the different hypotheses involved in a given case, the correct likelihood for the genetic evidence presented. However, it is exactly this stage of the testifying process that has caused a major controversy in recent years. The following sections will serve to summarize, and evaluate critically, the arguments put forward during that sometimes fierce debate.