This study proposes an extension to the discrete Laplace method and investigates the performance of the (extended) discrete Laplace method when used to assign match probabilities for haplotypes.
The discrete Laplace method can be used to estimate the frequency of a Y-chromosomal STR haplotype using a random sample from the population. The authors of this study show how the parameters to the extension of the model can be estimated by numerical optimisation using an off-the-shelf solver. Two limitations of the discrete Laplace method are the assumptions that each profile has exactly one allele at every locus and that this allele has an integer repeat number. The authors relax these assumptions to allow for multi-copy loci, partial repeats and null alleles. Concordance with the discrete Laplace method is obtained when the data satisfy the more stringent assumptions of the original method. The researchers also investigate the performance of the (extended) discrete Laplace method when used to assign match probabilities for haplotypes. A simulation study shows that as more loci are used, match probabilities are underestimated more severely. This is consistent with the hypothesis that the discrete Laplace method cannot model the matches that arise by being identical by descent (IBD). As the number of loci increases the fraction of matches that are IBD increases. Simulation provides support that the discrete Laplace can model those matches that arise from identity by state (IBS) only. (Published Abstract Provided)