In forensic casework it is common that multiple pieces of evidence are obtained in a single case. For the evaluation of such evidence, one cannot simply assume that they originated from the same source. If this can be disputed, one could decide to report the evidential value of the separate pieces by computing likelihood ratios (LRs) for them separately. However, by doing so, information regarding the conditional dependency structure is lost and the potentially difficult step of combining them is left to the trier of fact. Especially in situations where the pieces of evidence are of the same type, a combined evaluation could be substantially more informative. In such situations, it is not unrealistic that the separate evidential values are not optimally combined by the trier of fact. From a scientific point of view, the optimal way is that the forensic scientist combines the forensic evidence in a report using hypotheses at the 'activity level'. In practice, however, this is not always feasible for every case for reasons of efficiency. In this article, we explore what can be done in cases where the optimal solution is too costly. For a combined evaluation, the prior distribution for the number of distinct sources of the pieces of evidence becomes part of the LR. Generally, prior probabilities are beyond the scope of expertise of the forensic specialist and are left to the trier of fact to decide.Wepropose a lower bound LRapproach for such situations that is independent of the prior distribution. Using a set of examples, we present how this method can be applied in practice.

中文翻译：

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使用 LR 的下限组合多条证据

在法医案件工作中，在一个案件中获得多件证据是很常见的。对于此类证据的评估，不能简单地假设它们来自同一来源。如果这一点存在争议，人们可以决定通过分别计算它们的似然比 (LR) 来报告单独部分的证据价值。然而，通过这样做，关于条件依赖结构的信息丢失了，并且将它们组合起来的潜在困难步骤留给了事实的审判者。特别是在证据类型相同的情况下，综合评估可能会提供更多信息。在这种情况下，单独的证据价值没有被事实审判者最佳组合并不是不现实的。从科学的角度来说，最佳方法是法医科学家使用“活动级别”的假设将法医证据结合到报告中。然而，在实践中，出于效率的原因，这并不总是适用于所有情况。在本文中，我们将探讨在最优解决方案成本过高的情况下可以采取哪些措施。对于组合评估，证据的不同来源数量的先验分布成为 LR 的一部分。通常，先验概率超出了法医专家的专业范围，由事实审判者决定。我们针对这种情况提出了一种独立于先验分布的下限 LR 方法。使用一组示例，我们展示了如何在实践中应用这种方法。