The statistical evaluation of DNA mixtures with contributors from different ethnic groups

The effect of a structured population on the evaluation of forensic mixed stains has been considered by the authors and others. However, in countries with multiple racial or ethnic groups, it is not uncommon that contributors to a DNA mixture are of different ethnic groups. A famous example is the OJ Simpson case in which the suspect was an African-American, the victims were Caucasian Americans and the true perpetrator(s) could be from any ethnic group(s). In this paper six common mixture cases are considered and the formulae for likelihood ratios are derived. These formulae can help forensic DNA scientists acquire a better understanding of the problem. The effect of different ethnic groups is illustrated using a case in Hong Kong.