Evaluation of scientific evidence using Bayesian networks

Bayesian networks provide a valuable aid for representing epistemic relationships in a body of uncertain evidence. The paper proposes some simple Bayesian networks for standard analysis of patterns of inference concerning scientific evidence, with a discussion of the rationale behind the nets, the corresponding probabilistic formulas, and the required probability assessments.     

A general approach to Bayesian networks for the interpretation of evidence

Bayesian networks (BNs) are mathematically and statistically rigorous techniques for handling uncertainty. The field of forensic science has recently attributed increased attention to the many advantages of this graphical method for assisting the evaluation of scientific evidence. However, the majority of contributions that relate to this topic restrict themselves to the presentation of already "constructed" BNs, and often, only a few explanations are given as to how one obtains a specific BN structure for a given problem. Based on several examples, the present paper will therefore attempt to explain in more detail some guiding considerations that might be helpful for the elicitation of appropriate structures for BNs.     

Bayesian networks and the value of the evidence for the forensic two-trace transfer problem*

Forensic scientists face increasingly complex inference problems for evaluating likelihood ratios (LRs) for an appropriate pair of propositions. Up to now, scientists and statisticians have derived LR formulae using an algebraic approach. However, this approach reaches its limits when addressing cases with an increasing number of variables and dependence relationships between these variables. In this study, we suggest using a graphical approach, based on the construction of Bayesian networks (BNs). We first construct a BN that captures the problem, and then deduce the expression for calculating the LR from this model to compare it with existing LR formulae. We illustrate this idea by applying it to the evaluation of an activity level LR in the context of the two-trace transfer problem. Our approach allows us to relax assumptions made in previous LR developments, produce a new LR formula for the two-trace transfer problem and generalize this scenario to n traces.     

Logical evaluation of evidence when a person is suspected of committing two separate offences.

We consider the problem of drawing inferences within a legal framework when a person is a suspect for two separate offences. Although we are primarily concerned with scientific evidence the issue inevitably arises as to how that evidence interacts with other, non-scientific evidence. We show that, in this particular context, the evidence can be conveniently classified into three categories that concern, respectively: the first crime only; the second crime only; and evidence that relates to similarities between the two crimes. Two case examples are considered and we consider DNA, fibres and eyewitness evidence. These are viewed from the perspective of a prosecutor who has to decide whether or not to charge a suspect with one or both crimes. Graphical sensivity analyses are presented which have features that are not intuitively obvious.     

完善司法鉴定制度是科学证据时代的呼唤

司法鉴定是现代司法证明活动中查明案件事实的一种重要方法和手段.现代司法鉴定是司法证明方法进步的结果和体现.科学技术的进步使司法证明方法发生了两次重大的转变.以物证及其相关的鉴定结论等证据构成的"科学证据",应该成为司法证明最主要的手段.物证虽然是客观实在的,但其自身不能直接证明案件事实,需要人们的认识.司法鉴定是人们认识物证的途径.司法鉴定水平的提高可以帮助发现更多潜在的证据.科学技术是司法鉴定的生命.科学技术的进步是促进司法鉴定发展的最重要因素.司法鉴定制度改革应与审判体制改革相适应.司法鉴定制度改革应与证据法律制度相协调,既要赋予法官对鉴定结论的自由裁量权,又要对司法鉴定制度进行规范.司法鉴定制度改革应以提供"科学证据"为出发点,需要鉴定人出庭、技术方法标准化和建立行业协会等措施.     

非法证据排除中的“实质说理”与改革建议

关于非法证据排除规则,我国2012年《刑事诉讼法》确立了“非法言词与实物区别排除”,或者说,“强制排除与裁量排除相结合”的模式。当前,非法证据排除说理是整个刑事裁判文书说理的一个“短板”。在司法实践中,许多瑕疵证据、非法证据通过“补正”、“合理解释”被采纳,但缺乏“实质说理”。强化以审判为中心的诉讼制度改革,需要强化非法证据排除的“实质说理”。这一完善过程是艰巨的,涉及实体规则、程序规则、配套制度等方面的综合改革。从长远来看,有必要建构一独立自洽的针对证据合法性调查的“诉中诉”程序。     

Learning about Bayesian networks for forensic interpretation: an example based on the 'the problem of multiple propositions'

Both, Bayesian networks and probabilistic evaluation are gaining more and more widespread use within many professional branches, including forensic science. Notwithstanding, they constitute subtle topics with definitional details that require careful study. While many sophisticated developments of probabilistic approaches to evaluation of forensic findings may readily be found in published literature, there remains a gap with respect to writings that focus on foundational aspects and on how these may be acquired by interested scientists new to these topics. This paper takes this as a starting point to report on the learning about Bayesian networks for likelihood ratio based, probabilistic inference procedures in a class of master students in forensic science. The presentation uses an example that relies on a casework scenario drawn from published literature, involving a questioned signature. A complicating aspect of that case study - proposed to students in a teaching scenario - is due to the need of considering multiple competing propositions, which is an outset that may not readily be approached within a likelihood ratio based framework without drawing attention to some additional technical details. Using generic Bayesian networks fragments from existing literature on the topic, course participants were able to track the probabilistic underpinnings of the proposed scenario correctly both in terms of likelihood ratios and of posterior probabilities. In addition, further study of the example by students allowed them to derive an alternative Bayesian network structure with a computational output that is equivalent to existing probabilistic solutions. This practical experience underlines the potential of Bayesian networks to support and clarify foundational principles of probabilistic procedures for forensic evaluation.     

The evaluation of evidence in the forensic investigation of fire incidents (Part I): an approach using Bayesian networks

The forensic investigation of the origin and cause of a fire incident is a particularly demanding area of expertise. As the available evidence is often incomplete or vague, uncertainty is a key element. The present study is an attempt to approach this through the use of Bayesian networks, which have been found useful in assisting human reasoning in a variety of disciplines in which uncertainty plays a central role. The present paper describes the construction of a Bayesian network (BN) and its use for drawing inferences about propositions of interest, based upon a single, possibly non replicable item of evidence: detected residual quantities of a flammable liquid in fire debris.     

A probabilistic approach to the joint evaluation of firearm evidence and gunshot residues

The present paper addresses issues that affect both the separate as well as the joint evaluation of firearm evidence (i.e., marks) and gunshot residues (GSR). Mark evidence will be used as a basis to discriminate among barrels through which a bullet in question might have been shot whereas GSR will be used to draw inferences about the distance of firing. Particular attention is drawn to the coherent handling of uncertainties associated with the various parameters considered within each item of evidence. The proposed analysis relies on a probabilistic viewpoint that uses graphical models (i.e., Bayesian networks) as an aid to cope with the complexity induced by the number of variables considered. The paper discusses how an approach based on a probabilistic network environment can be used for the formal analysis and construction of arguments. Emphasis is made on the gain of insight into structural dependencies that may be uncovered when the evaluative process is extended beyond single items of scientific evidence.     

Bayesian framework for the evaluation of fiber evidence in a double murder--a case report

Fiber evidence found on a suspect vehicle was the only useful trace to reconstruct the dynamics of the transportation of two corpses. Optical microscopy, UV-Vis microspectrophotometry and infrared analysis were employed to compare fibers recovered in the trunk of a car to those of the blankets composing the wrapping in which the victims had been hidden. A "pseudo-1:1" taping permitted to reconstruct the spatial distribution of the traces and to further strengthen the support to one of the hypotheses. The Likelihood Ratio (LR) was calculated, in order to quantify the support given by forensic evidence to the explanations proposed. A generalization of the Likelihood Ratio equation to cases analogous to this has been derived. Fibers were the only traces that helped in the corroboration of the crime scenario, being absent any DNA, fingerprints and ballistic evidence.     

The evaluation of evidence in the forensic investigation of fire incidents. Part II. Practical examples of the use of Bayesian networks

This paper extends a previous discussion of the use of Bayesian networks for evaluating evidence in the forensic investigation of fire incidents. Bayesian networks are proposed for two casework examples and the practical implications studied in detail. Such networks were found to provide precious support in addressing some of the wide range of issues that affect the coherent evaluation of evidence.     

Bayesian analysis and the accumulation of evidence in crime and justice intervention studies

In recent years a great deal of attention has turned to the need for policy-relevant research in criminology. Methodologically, attention has been trained on the use of randomized experimental designs and cumulative systematic reviews of evidence to accomplish this goal. Our work here reviews and demonstrates the utility of the Bayesian analytic framework, in the context of crime prevention and justice treatment studies, as a means of furthering the goals of research synthesis and creation of policy-relevant scientific statements. Evidence from various fields is used as a foundation for the discussion, and an empirical example illustrates how this approach might be useful in practical criminological research. It is concluded that Bayesian analysis offers a useful complement to existing approaches and warrants further inclusion in the ongoing discussion about how best to assess program effectiveness, synthesize evidence, and report findings from crime and justice evaluations in a way that is relevant to policy makers and practitioners.

Paternity probability when a relative of the father is an alleged father

When scientists use DNA evidence in court, coancestry effects such as population structure and relatedness are usually ignored. In paternity cases, only if a particular man has the child's paternal allele at a certain locus, can he not be excluded in the paternity dispute. However, it is certainly true that close relatives will be far more likely to have the child's paternal allele than will random members of the reference population. In particular, the probability that the true father's brother has the paternal allele is very much greater than that for any other relationship. In this paper, the authors describe a method for inference in a case where the true father may be a relative of the alleged father. This paper also reports that most current methods overstate the probability that the alleged father is the father.     

Beliefs about secondary confession evidence: a survey of laypeople and defense attorneys

We surveyed students, community members, and defense attorneys regarding beliefs about secondary confession evidence (i.e. when a third party tells authorities that a person has confessed to him or her) from jailhouse informants and other sources. Results indicated that laypeople perceive secondary confessions as less credible than other types of evidence (e.g. forensics, DNA, eyewitness testimony), and they are knowledgeable about factors that may influence the veracity of secondary confessions, such as incentives or previous testimony. However, they underestimated or were uncertain about how persuasive secondary confessions would be to themselves or other jurors. Compared to laypeople, defense attorneys were more sensitive about issues affecting the reliability of secondary confessions.     

Human trafficking for labour exploitation: the results of a two-phase systematic review mapping the European evidence base and synthesising key scientific research evidence

Objectives

Our objectives were (1) to systematically map the contours of the European evidence base on labour trafficking, identifying its key characteristics, coverage, gaps, strengths and weaknesses and (2) to synthesise key scientific research.

Methods

We took a two-phase approach: a systematic map followed by a detailed synthesis of key scientific research evidence. Our search strategy included 15 databases, hand searches of additional journals, backwards searches, snowball searches and expert recommendations. We identified and screened 6106 records, mapped 152 and synthesised eight.

Results

Overall, the literature was limited and fragmented. Reports produced by official agencies dominated; academic authorship and peer-reviewed outputs were comparatively rare. Few publications met minimum scientific standards. Qualitative designs outweighed quantitative ones. Publications typically described trafficking’s problem profile and/or discussed interventions; they rarely assessed trafficking’s impacts or evaluated interventions. Even among the key scientific research, the quality of evidence was variable and often low. Particular weaknesses included poor methods reporting, unclear or imprecise results and conclusions not properly grounded in the data. The synthesised studies were all exploratory, also sharing other design features. Common themes identified included: poor treatment of victims; diversity of sectors affected and commonalities among victims; inadequacies of current responses; and barriers to interventions.

Conclusions

There is a lack of high-quality studies into European labour trafficking. Methodological opacity, insufficient rigour and publication in non-indexed locations impede the identification, assessment and synthesis of evidence. Adherence to higher reporting standards would further the field’s development and particular research gaps should be addressed.

     

试点成效明显改革任重道远——关于第一批监狱体制改革试点工作的实践思考

按照2003年1月((国务院批转司法部关于监狱体制改革试点工作指导意见的通知》的要求，自2003年2月开始，司法部决定在黑龙江、江西、上海、湖北、重庆、陕西6省市进行我国第一批监狱体制改革试点。两年来，监狱体制改革试点工作总体上进展顺利。为了全面检查改革试点情况，总结推广好的经验和做法，2004年12月，笔者参加了司法部组织的检查组，对六省(市)监狱体制改革试点工作进行了为期一个月的检查。通过实地的检查、调研以及近年来参与改革试点的相关工作的感悟，印象较深、感想较多，感到有必要进行总结反思，以便为下一步健康有序地稳步推进监狱体制改革试点工作提供一些参考建议，并愿与关心监狱体制改革工作的同仁们进行探讨交流。