Dipartimento di Chimica, Università degli Studi di Torino, Via P. Giuria 7, 10125, Torino, Italy; Centro Regionale Antidoping e di Tossicologia "A. Bertinaria", Regione Gonzole 10/1, 10043, Orbassano, Torino, Italy.
Centro Regionale Antidoping e di Tossicologia "A. Bertinaria", Regione Gonzole 10/1, 10043, Orbassano, Torino, Italy.
Forensic Sci Int Genet. 2018 Nov;37:143-150. doi: 10.1016/j.fsigen.2018.08.002. Epub 2018 Aug 3.
The present study investigated the capabilities and performances of semi-continuous and fully-continuous probabilistic approaches to DNA mixtures interpretation, particularly when dealing with Low-Template DNA mixtures. Five statistical interpretation software, such as Lab Retriever and LRmix Studio - involving semi-continuous algorithms - and DNA•VIEW, EuroForMix and STRmix- employing fully-continuous formulae - were employed to calculate likelihood ratio, comparing the prosecution and the defense hypotheses relative to a series of on-purpose prepared DNA mixtures that respectively contained 2 and 3 known contributors. National Institute of Standards and Technologies (NIST) certified templates were used for samples set up, which contained different DNA amounts for each contributor. 2-person mixtures have been prepared with proportions equal to 1:1, 19:1 and 1:19 in terms of DNA concentration. Conversely, three person mixtures were constituted by proportions equal to 20:9:1, 8:1:1, 6:3:1 and 1:1:1 in terms of DNA concentration. Furthermore, 8 equally-proportioned 3-person mixtures were prepared by means of scalar dilutions starting from an overall amount of 0.500 ng, then ranging up to DNA samples with concentrations equal to 0.004 ng (i.e. Low-Template DNA). DNA mixtures were set up in triplicate and amplified with 7 DNA amplification kits (i.e. GlobalFiler PCR Amplification Kit, NGM SElect PCR Amplification Kit, MiniFiler PCR Amplification Kit, Power Plex Fusion, PowerPlex 6C Matrix System, Power Plex ESI 17 Fast and Power Plex ESX 17 Fast) in order to evaluate whether the selection of a certain kit might represent a bias factor, capable of altering the whole interpretation process. A multi-software approach helped us to highlight any trend in the likelihood ratio results provided by semi- and fully-continuous software. As a matter of fact, fully-continuous computations provided different (higher) results in terms of degrees of magnitude of the likelihood ratio values with respect to those from the semi-continuous approach, regardless of the amplification kit that was utilized.
本研究调查了半连续和全连续概率方法在 DNA 混合物解释方面的能力和性能，特别是在处理低模板 DNA 混合物时。使用了五种统计解释软件，例如 LabRetriever 和 LRmix Studio（涉及半连续算法）以及 DNA•VIEW、EuroForMix 和 STRmix（采用全连续公式），以计算似然比，比较起诉方和辩护方相对于一系列有目的制备的 DNA 混合物的假设，这些混合物分别包含 2 个和 3 个已知供体。使用国家技术标准研究院 (NIST) 认证的模板来设置样本，其中每个供体的 DNA 含量不同。2 人混合物的制备比例分别为 1:1、19:1 和 1:19（按 DNA 浓度计）。相反，三人混合物的构成比例分别为 20:9:1、8:1:1、6:3:1 和 1:1:1（按 DNA 浓度计）。此外，通过从总体量 0.500ng 开始的标量稀释制备了 8 个等比例的三人混合物，然后范围扩大到 DNA 浓度等于 0.004ng 的 DNA 样本（即低模板 DNA）。DNA 混合物一式三份设置，并使用 7 种 DNA 扩增试剂盒（即 GlobalFiler PCR 扩增试剂盒、NGM SElect PCR 扩增试剂盒、MiniFiler PCR 扩增试剂盒、PowerPlex Fusion、PowerPlex 6C Matrix System、PowerPlex ESI 17 Fast 和 PowerPlex ESX 17 Fast）进行扩增，以评估选择特定试剂盒是否可能成为改变整个解释过程的偏倚因素。多软件方法帮助我们突出了半连续和全连续软件提供的似然比结果中的任何趋势。事实上，全连续计算提供了不同（更高）的结果，即似然比值的数量级相对于半连续方法，而不管使用的扩增试剂盒如何。
