Significance of micro-geographical population structure in forensic cases: a bayesian exploration
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- Zarrabeitia, M.T., Riancho, J.A., Lareu, M.V. et al. Int J Legal Med (2003) 117: 302. doi:10.1007/s00414-003-0372-9
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We studied the influence of population structure at the microgeographical level on the analysis of forensic cases. A total of nine autosomal STRs and seven Y-STRs were analyzed in the general mixed population and in two relatively isolated valleys of Cantabria, a region in Northern Spain. Statistically significant differences existed in the frequency distribution of four autosomal STRs, with an overall Fst value of 0.3%. A simulation of virtual trio cases revealed that it did not have a practical influence on the analysis of paternity disputes. Significant differences also existed in most Y-STRs, with an overall Fst value of 3%. Thus, using the general database instead of the specific valley database resulted in 5-fold or higher overestimation of the likelihood ratio of matching in up to 30% of cases. A bayesian analysis revealed that this had a significant impact on the estimation of the probability of identity in scenarios of low "a priori" odds of suspicion.