Human Rights Center, U.C. Berkeley, Berkeley, CA, United States; DNA·VIEW, 6801 Thornhill Drive, Oakland, CA 94611-1336, United States.
Forensic Sci Int Genet. 2014 Jan;8(1):233-43. doi: 10.1016/j.fsigen.2013.10.007. Epub 2013 Nov 8.
The Y haplotype population-genetic terrain is better explored from a fresh perspective rather than by analogy with the more familiar autosomal ideas. For haplotype matching probabilities, versus for autosomal matching probabilities, explicit attention to modelling - such as how evolution got us where we are - is much more important while consideration of population frequency is much less so. This paper explores, extends, and explains some of the concepts of "Fundamental problem of forensic mathematics - the evidential strength of a rare haplotype match". That earlier paper presented and validated a "kappa method" formula for the evidential strength when a suspect matches a previously unseen haplotype (such as a Y-haplotype) at the crime scene. Mathematical implications of the kappa method are intuitive and reasonable. Suspicions to the contrary raised in rest on elementary errors. Critical to deriving the kappa method or any sensible evidential calculation is understanding that thinking about haplotype population frequency is a red herring; the pivotal question is one of matching probability. But confusion between the two is unfortunately institutionalized in much of the forensic world. Examples make clear why (matching) probability is not (population) frequency and why uncertainty intervals on matching probabilities are merely confused thinking. Forensic matching calculations should be based on a model, on stipulated premises. The model inevitably only approximates reality, and any error in the results comes only from error in the model, the inexactness of the approximation. Sampling variation does not measure that inexactness and hence is not helpful in explaining evidence and is in fact an impediment. Alternative haplotype matching probability approaches that various authors have considered are reviewed. Some are based on no model and cannot be taken seriously. For the others, some evaluation of the models is discussed. Recent evidence supports the adequacy of the simple exchangability model on which the kappa method rests. However, to make progress toward forensic calculation of Y haplotype mixture evidence a different tack is needed. The "Laplace distribution" model of Andersen et al. [3] which estimates haplotype frequencies by identifying haplotype clusters in population data looks useful.
从全新的视角而非通过类比更熟悉的常染色体概念来探索 Y 单倍型群体遗传地形会更好。对于单倍型匹配概率，而非常染色体匹配概率，更重要的是明确注意建模，例如进化如何使我们走到现在的位置，而对群体频率的考虑则不那么重要。本文探讨、扩展和解释了“法医学基本问题——罕见单倍型匹配的证据强度”一文中的一些概念。更早的那篇论文提出并验证了一种“kappa 方法”公式，用于计算在犯罪现场嫌疑人与以前未见的单倍型（如 Y 单倍型）匹配时的证据强度。kappa 方法的数学含义直观且合理。相反的怀疑意见是基于基本错误。推导出 kappa 方法或任何合理的证据计算的关键是理解思考单倍型群体频率是一种误导；关键问题是匹配概率。但不幸的是，在法医界的很大一部分中，这两种概念之间存在混淆。示例清楚地说明了为什么（匹配）概率不是（群体）频率，以及为什么匹配概率的不确定区间只是混乱的思维。法医匹配计算应该基于模型，基于规定的前提。该模型不可避免地仅近似于现实，并且结果中的任何误差仅来自模型误差，即逼近的不准确性。抽样变化并不能衡量这种不准确性，因此无助于解释证据，实际上是一种障碍。本文还回顾了不同作者考虑的各种替代单倍型匹配概率方法。有些方法没有基于模型，因此不能认真对待。对于其他方法，讨论了一些对模型的评估。最近的证据支持 kappa 方法所依据的简单可交换模型的充分性。然而，要朝着法医计算 Y 单倍型混合物证据的方向取得进展，需要采取不同的策略。Andersen 等人的“Laplace 分布”模型[3]通过在群体数据中识别单倍型簇来估计单倍型频率，看起来很有用。
