Université de Lyon, Université Lyon 1, CNRS, UMR 5558, Laboratoire de biométrie et biologie évolutive, 69622 Villeurbanne, France.
Forensic Sci Int Genet. 2011 Aug;5(4):281-4. doi: 10.1016/j.fsigen.2010.04.005. Epub 2010 May 20.
We propose to quantify the accuracy of a likelihood-based estimator that was recently proposed for the determination of the number of contributors to a DNA mixture, when genetic data alone is considered [H. Haned, L. Pène, J.R. Lobry, A.B. Dufour, D. Pontier, Estimating the number of contributors to forensic DNA mixtures: does maximum likelihood perform better than maximum allele count? J. Forensic Sci., in press]. Using Bayes' theorem, we derive a formula for the calculation of the predictive value (PV) of the likelihood-based estimator. The PV gives the probability that a DNA stain contains the DNAs of i people given that the maximum likelihood estimator gave an estimate of i contributors for this stain. We illustrate the PV calculations for two different types of DNA evidence: traces and body fluids. The PV varied according to the number of contributors involved in the DNA stain. Setting the maximum number of possible contributors to five, the lowest predictive values were scored for five-person mixtures with a minimum value of 0.26 for traces, but values were always above 0.94 for stains comprising one, two or three contributors, for both traces and body fluids. Values remained relatively high for four-person mixtures with a minimum value of 0.69. These findings confirm that likelihood-maximization is a powerful approach for the determination of the number of contributors to forensic DNA mixtures.
我们提出了一种基于可能性的估计器的准确性的量化方法，该方法最近被提出用于确定 DNA 混合物中贡献者的数量，当仅考虑遗传数据时[H. Haned、L. Pène、J.R. Lobry、A.B. Dufour、D. Pontier，用于法医 DNA 混合物中贡献者数量的估计：最大似然比最大等位基因计数表现更好吗？法医科学，即将出版]。使用贝叶斯定理，我们推导出了用于计算基于可能性的估计器的预测值 (PV) 的公式。PV 给出了 DNA 痕迹包含 i 个人的 DNA 的概率，前提是最大似然估计器对该痕迹给出了 i 个贡献者的估计。我们针对两种不同类型的 DNA 证据：痕迹和体液，说明了 PV 的计算。PV 根据 DNA 痕迹中涉及的贡献者数量而变化。将可能的最大贡献者数量设置为五个，对于五人混合，最低的预测值为 0.26（对于痕迹），但对于包含一个、两个或三个贡献者的痕迹和体液，值始终高于 0.94。对于四人混合，值仍相对较高，最小值为 0.69。这些发现证实了似然最大化是确定法医 DNA 混合物中贡献者数量的一种强大方法。
