Worldwide [Image: see text] Estimates Relative to Five Continental-Scale Populations

We estimate the population genetics parameter [Image: see text] (also referred to as the fixation index) from short tandem repeat (STR) allele frequencies, comparing many worldwide human subpopulations at approximately the national level with continental-scale populations. [Image: see text] is commonly used to measure population differentiation, and is important in forensic DNA analysis to account for remote shared ancestry between a suspect and an alternative source of the DNA. We estimate [Image: see text] comparing subpopulations with a hypothetical ancestral population, which is the approach most widely used in population genetics, and also compare a subpopulation with a sampled reference population, which is more appropriate for forensic applications. Both estimation methods are likelihood-based, in which [Image: see text] is related to the variance of the multinomial-Dirichlet distribution for allele counts. Overall, we find low [Image: see text] values, with posterior 97.5 percentiles [Image: see text] when comparing a subpopulation with the most appropriate population, and even for inter-population comparisons we find [Image: see text] [Image: see text]. These are much smaller than single nucleotide polymorphism-based inter-continental [Image: see text] estimates, and are also about half the magnitude of STR-based estimates from population genetics surveys that focus on distinct ethnic groups rather than a general population. Our findings support the use of [Image: see text] up to 3% in forensic calculations, which corresponds to some current practice.