Hicks T, Biedermann A, de Koeijer J A, Taroni F, Champod C, Evett I W
School of Criminal Justice, University of Lausanne, 1015 Dorigny, Switzerland; Fondation pour la formation continue universitaire lausannoise (UNIL-EPFL), 1015 Dorigny, Switzerland.
School of Criminal Justice, University of Lausanne, 1015 Dorigny, Switzerland; Fondation pour la formation continue universitaire lausannoise (UNIL-EPFL), 1015 Dorigny, Switzerland.
Sci Justice. 2015 Dec;55(6):520-5. doi: 10.1016/j.scijus.2015.06.008. Epub 2015 Jul 14.
The value of forensic results crucially depends on the propositions and the information under which they are evaluated. For example, if a full single DNA profile for a contemporary marker system matching the profile of Mr A is assessed, given the propositions that the DNA came from Mr A and given it came from an unknown person, the strength of evidence can be overwhelming (e.g., in the order of a billion). In contrast, if we assess the same result given that the DNA came from Mr A and given it came from his twin brother (i.e., a person with the same DNA profile), the strength of evidence will be 1, and therefore neutral, unhelpful and irrelevant(1) to the case at hand. While this understanding is probably uncontroversial and obvious to most, if not all practitioners dealing with DNA evidence, the practical precept of not specifying an alternative source with the same characteristics as the one considered under the first proposition may be much less clear in other circumstances. During discussions with colleagues and trainees, cases have come to our attention where forensic scientists have difficulty with the formulation of propositions. It is particularly common to observe that results (e.g., observations) are included in the propositions, whereas-as argued throughout this note-they should not be. A typical example could be a case where a shoe-mark with a logo and the general pattern characteristics of a Nike Air Jordan shoe is found at the scene of a crime. A Nike Air Jordan shoe is then seized at Mr A's house and control prints of this shoe compared to the mark. The results (e.g., a trace with this general pattern and acquired characteristics corresponding to the sole of Mr A's shoe) are then evaluated given the propositions 'The mark was left by Mr A's Nike Air Jordan shoe-sole' and 'The mark was left by an unknown Nike Air Jordan shoe'. As a consequence, the footwear examiner will not evaluate part of the observations (i.e., the mark presents the general pattern of a Nike Air Jordan) whereas they can be highly informative. Such examples can be found in all forensic disciplines. In this article, we present a few such examples and discuss aspects that will help forensic scientists with the formulation of propositions. In particular, we emphasise on the usefulness of notation to distinguish results that forensic scientists should evaluate from case information that the Court will evaluate.
法医鉴定结果的价值在很大程度上取决于评估时所依据的命题和信息。例如，对于一个当代标记系统的完整单倍体DNA图谱，若其与A先生的图谱匹配，在DNA来自A先生和DNA来自一个未知人员这两个命题下进行评估，证据的强度可能是压倒性的（例如，达到十亿分之一的量级）。相比之下，如果在DNA来自A先生和DNA来自他的双胞胎兄弟（即具有相同DNA图谱的人）这两个命题下评估相同的结果，证据强度将为1，因此是中性的、无帮助的且与手头案件无关(1)。虽然这种理解对于大多数（如果不是所有）处理DNA证据的从业者来说可能是无可争议且显而易见的，但在其他情况下，不指定与第一个命题所考虑的具有相同特征的替代来源这一实际准则可能就不那么清晰了。在与同事和实习生的讨论中，我们注意到一些案例，其中法医科学家在命题的制定上存在困难。特别常见的是观察到结果（例如观察数据）被包含在命题中，而正如本说明通篇所主张的，它们不应该被包含。一个典型的例子可能是在犯罪现场发现一个带有耐克飞人乔丹鞋标志和一般图案特征的鞋印。然后在A先生家中查获了一双耐克飞人乔丹鞋，并将这双鞋的对照印记与鞋印进行比对。接着在“该鞋印是由A先生的耐克飞人乔丹鞋底留下的”和“该鞋印是由一双未知的耐克飞人乔丹鞋留下的”这两个命题下评估结果（例如，一个具有这种一般图案且获得的特征与A先生鞋底对应的痕迹）。结果，鞋类检验员不会评估部分观察数据（即鞋印呈现出耐克飞人乔丹鞋的一般图案），而这些数据可能具有很高的信息量。此类例子在所有法医领域都能找到。在本文中，我们给出一些这样的例子，并讨论有助于法医科学家制定命题的各个方面。特别是，我们强调使用符号来区分法医科学家应评估的结果和法庭将评估的案件信息的有用性。
