Biedermann A, Taroni F, Bozza S, Augsburger M, Aitken C G G
University of Lausanne, School of Criminal Justice, 1015 Lausanne-Dorigny, Switzerland.
University of Lausanne, School of Criminal Justice, 1015 Lausanne-Dorigny, Switzerland.
Forensic Sci Int. 2018 Jul;288:72-80. doi: 10.1016/j.forsciint.2018.04.030. Epub 2018 Apr 25.
In this paper we critically discuss the definition and use of cut-off values by forensic scientists, for example in forensic toxicology, and point out when and why such values - and ensuing categorical conclusions - are inappropriate concepts for helping recipients of expert information with their questions of interest. Broadly speaking, a cut-off is a particular value of results of analyses of a target substance (e.g., a toxic substance or one of its metabolites in biological sample from a person of interest), defined in a way such as to enable scientists to suggest conclusions regarding the condition of the person of interest. The extent to which cut-offs can be reliably defined and used is not unanimously agreed within the forensic science community, though many practitioners - especially in operational laboratories - rely on cut-offs for reasons such as ease of use and simplicity. In our analysis, we challenge this practice by arguing that choices made for convenience should not be to the detriment of balance and coherence. To illustrate our discussion, we will choose the example of alcohol markers in hair, used widely by forensic toxicologists to reach conclusions regarding the drinking behaviour of individuals. Using real data from one of the co-authors' own work and recommendations of cut-offs published by relevant professional organisations, we will point out in what sense cut-offs are incompatible with current evaluative guidelines (e.g., [31]) and show how to proceed logically without cut-offs by using a standard measure for evidential value. Our conclusions run counter to much current practice, but are inevitable given the inherent definitional and conceptual shortcomings of scientific cut-offs. We will also point out the difference between scientific cut-offs and legal thresholds and argue that the latter - but not the former - are justifiable and can be dealt with in logical evaluative procedures.
在本文中，我们批判性地讨论了法医科学家对临界值的定义和使用，例如在法医毒理学领域，并指出在何时以及为何这些值——以及随之而来的分类结论——对于帮助专家信息接收者解决他们感兴趣的问题而言是不合适的概念。广义而言，临界值是目标物质（例如，来自相关人员生物样本中的有毒物质或其代谢物之一）分析结果的一个特定值，其定义方式使科学家能够就相关人员的状况得出结论。尽管许多从业者——尤其是在操作实验室中——出于易用性和简单性等原因依赖临界值，但法医科学界对于临界值能够被可靠定义和使用的程度并未达成一致。在我们的分析中，我们对这种做法提出质疑，认为为了方便而做出的选择不应损害平衡性和连贯性。为了说明我们的讨论，我们将选择头发中酒精标志物的例子，法医毒理学家广泛使用该例子来得出关于个人饮酒行为的结论。利用其中一位共同作者自己工作中的实际数据以及相关专业组织公布的临界值建议，我们将指出临界值在何种意义上与当前的评估指南（例如，[31]）不兼容，并展示如何通过使用证据价值的标准度量在不使用临界值的情况下进行逻辑推理。我们的结论与当前的许多做法背道而驰，但鉴于科学临界值在定义和概念上的固有缺陷，这是不可避免的。我们还将指出科学临界值与法律阈值之间的区别，并认为后者——而非前者——是合理的，并且可以在逻辑评估程序中进行处理。
