Evaluation of parentage testing accuracy of child trafficking cases: Combining the exclusion probability and likelihood ratio approaches

The Chinese government established a national anti-trafficking DNA database in 2009 to help reunite trafficked children with their families. The database collects DNA information from missing children's parents, trafficked and homeless children, then conducts parentage testing using 18 or more loci to find matched pairs. This article evaluates the matching accuracy of parentage testing in child-trafficking cases, under both Hardy-Weinberg equilibrium and population substructure. Both one-parent and two-parent scenarios are considered, and mutations are taken into account. The number of random matches is first evaluated using exclusion probability (PE). It is found that there are a large number of single parent-child pairs that match at 18 loci, but the PE approach cannot tell which are the true positive ones. The likelihood ratio (LR) approach can help distinguish the true positive matches. So the second step is to obtain the true positive rate and false positive rate of matched pairs of single parent and child according to the LR approach. Based on the results of the two-step procedure, it is concluded that more than 18 loci should be used to ensure a correct match of single parent and child.