论文标题
关于混合DNA概况证据的概率主张的局限性
On the limitations of probabilistic claims about the probative value of mixed DNA profile evidence
论文作者
论文摘要
似然比（LR）是确定法医匹配证据强度的常用措施。当法医专家确定在犯罪现场发现的DNA的高LR时，与嫌疑人的DNA概况相匹配时，他们通常会报告“这为检方假设DNA来自犯罪嫌疑人提供了强有力的支持。但是，即使使用高LR，如果用于确定LR的防御假设不是起诉假设的否定，则证据也可能无法支持起诉假设（例如，当替代方案是“ DNA是来自与被告无关的人）而不是'DNA的人时，DNA不是来自嫌疑人的DNA'）。对于DNA混合物曲线，尤其是低模板DNA（LTDNA），对于“匹配”的高LR的值 - 通常是根据概率基因分型软件计算得出的 - 尤其值得怀疑。但这不仅是因为在这种情况下使用了非详尽的假设。与单轮廓DNA“匹配”相反，唯一的残留不确定性是，嫌疑人以外的其他人是否具有相同的匹配DNA谱，即使没有任何贡献者都具有DNA谱，但可疑DNA谱的所有基因型都可以出现在DNA混合物的每个位置上。实际上，在没有其他证据的情况下，我们表明，即使包括可疑嫌疑人的后验概率非常低，也可能对假设“可疑嫌疑人”具有很高的LR。然而，在这种情况下，法医专家通常仍将高LR报告为“对犯罪嫌疑人是贡献者的强烈支持”。我们的观察结果表明，在某些情况下，LR的使用可能导致律师和陪审员严重高估了LTDNA混合概况“匹配”的证明价值
The likelihood ratio (LR) is a commonly used measure for determining the strength of forensic match evidence. When a forensic expert determines a high LR for DNA found at a crime scene matching the DNA profile of a suspect they typically report that 'this provides strong support for the prosecution hypothesis that the DNA comes from the suspect'. However, even with a high LR, the evidence might not support the prosecution hypothesis if the defence hypothesis used to determine the LR is not the negation of the prosecution hypothesis (such as when the alternative is 'DNA comes from a person unrelated to the defendant' instead of 'DNA does not come from the suspect'). For DNA mixture profiles, especially low template DNA (LTDNA), the value of a high LR for a 'match' - typically computed from probabilistic genotyping software - can be especially questionable. But this is not just because of the use of non-exhaustive hypotheses in such cases. In contrast to single profile DNA 'matches', where the only residual uncertainty is whether a person other than the suspect has the same matching DNA profile, it is possible for all the genotypes of the suspect's DNA profile to appear at each locus of a DNA mixture, even though none of the contributors has that DNA profile. In fact, in the absence of other evidence, we show it is possible to have a very high LR for the hypothesis 'suspect is included in the mixture' even though the posterior probability that the suspect is included is very low. Yet, in such cases a forensic expert will generally still report a high LR as 'strong support for the suspect being a contributor'. Our observations suggest that, in certain circumstances, the use of the LR may have led lawyers and jurors into grossly overestimating the probative value of a LTDNA mixed profile 'match'
