Dørum Guro, Bleka Øyvind, Gill Peter, Haned Hinda, Snipen Lars, Sæbø Solve, Egeland Thore
Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences (UMB), Norway.
Department of Forensic Genetics, Norwegian Institute of Public Health, Oslo, Norway.
Forensic Sci Int Genet. 2014 Mar;9:93-101. doi: 10.1016/j.fsigen.2013.11.008. Epub 2013 Dec 9.
If complex DNA profiles, conditioned on multiple individuals are evaluated, it may be difficult to assess the strength of the evidence based on the likelihood ratio. A likelihood ratio does not give information about the relative weights that are provided by separate contributors. Alternatively, the observed likelihood ratio can be evaluated with respect to the distribution of the likelihood ratio under the defense hypothesis. We present an efficient algorithm to compute an exact distribution of likelihood ratios that can be applied to any LR-based model. The distribution may have several applications, but is used here to compute a p-value that corresponds to the observed likelihood ratio. The p-value is the probability that a profile under the defense hypothesis, substituted for a questioned contributor e.g. suspect, would attain a likelihood ratio which is at least the same magnitude as that observed. The p-value can be thought of as a scaled version of the likelihood ratio, giving a quantitative measure of the strength of the evidence relative to the specified hypotheses and the model used for the analysis. The algorithm is demonstrated on examples based on real data. R code for the algorithm is freely available in the R package euroMix.
如果对基于多个个体的复杂DNA图谱进行评估，那么基于似然比来评估证据的强度可能会很困难。似然比并未给出关于不同贡献者所提供的相对权重的信息。另外，可以根据辩方假设下似然比的分布来评估观察到的似然比。我们提出了一种高效算法，用于计算可应用于任何基于似然比模型的似然比的精确分布。该分布可能有多种应用，但在此用于计算与观察到的似然比相对应的p值。p值是指在辩方假设下，用例如嫌疑人等被质疑的贡献者替代后的图谱获得至少与观察到的似然比相同大小的似然比的概率。p值可以被视为似然比的一种缩放形式，它给出了相对于指定假设和用于分析的模型的证据强度的定量度量。该算法在基于实际数据的示例上进行了演示。该算法的R代码可在R包euroMix中免费获取。
