Bayesian networks for the interpretation of biological evidence

Abstract

In court, it is typical for biological evidence to be reported at a level that only addresses how likely the DNA evidence is if it originated from a particular individual, or individuals. However, there are other questions that could be considered that would be of value in enabling the court, including the jury, to make better informed decisions. For example, although answers to specific questions such as: “Which type of bodily fluid has the DNA originated from?” or, “How was the DNA deposited at the scene?” would be probabilistic in nature, they can be crucial to the outcome of a case. The relationship between the DNA evidence, the source of the DNA and the activity that took place is described in a term called the “hierarchy of propositions.” Currently, such questions are usually answered by scientists subjectively with little to no logical framework to assist them. Bayesian networks have proven to be beneficial in providing logical reasoning by way of a likelihood ratio to help combine subjective, yet, experience‐based, opinions of experts with experimental data when answering questions which can be both complex and uncertain. These networks offer a framework that provides balance, transparency, and robustness in the evaluation of evidence. A current limitation of the use of Bayesian networks includes a lack of understanding of the underlying concepts from both forensic scientists and the courts and consequently a reduced recognition of the potential strengths. This article is categorized under: Forensic Biology > Interpretation of Biological Evidence

Direct and Secondary Transfer of Touch DNA on a Credit Card: Evidence Evaluation Given Activity Level Propositions and Application of Bayesian Networks

“…It is recommended that the expert opinion is informed by empirical and experimental data, present in the literature or produced in-house. Given the high number of case-specific relevant variables and of data regarding the activities that may have led to the deposition and transfer of DNA, the experts are increasingly relying on the use of Bayesian Networks (BN) [38,[44][45][46][47][48]. BNs are graphical representations of the case that include all the relevant variables and display their dependency relationships and interactions.…”

Recent advances in forensic biology and forensic DNA typing: INTERPOL review 2019–2022

“…Following a comprehensive January 2019 review that cited [ 298 ] references on DNA-TPPR [ 14 ], the same authors provided an update in November 2021 on recent progress towards meeting challenges and a synopsis of 144 relevant articles published between January 2018 and March 2021 [ 297 ]. While few studies provide the information needed to help assign probabilities of obtaining DNA results given specific sets of circumstances, progress includes use of Bayesian Networks [ 300 ] to identify variables for complex transfer scenarios [ 38 , [301] , [302] , [303] , [304] , [305] ] as well as development of an online database DNA-TrAC 43 for relevant research articles [ 299 ] and a structured knowledge base 44 with information to help practitioners interpret general transfer events at an activity level [ 306 ].…”

Towards another paradigm for forensic science?

“…Indeed, in this model of updating beliefs, the LR takes into account all the information that has been communicated to the scientist in the context of the case, but is also implicitly supposed to include those to which they would have had access, either legally or not by their employment position, training, experience or civil life (e.g., information in the press) (Dror, 2020a; Whitman & Koppl, 2010). Even though the debate has remained lively on this decision, it is doubtful that Bayes' theorem, presented as the mathematical quintessence of this transparency, is sufficient to satisfy this expected quality (Aitken et al, 2011; Aitken & Taroni, 2004; Biedermann & Taroni, 2006a, 2002; Dawid, 2002; Dawid et al, 2011; Fenton et al, 2013; Finkelstein & Fairley, 1970; Hahn, 2014; Jackson et al, 2015; Roberts & Aitken, 2014; Robertson et al, 2016; Schaapveld et al, 2019; Sironi et al, 2016; Smit et al, 2016; Taroni et al, 2004). Considering the LR as encompassing implicitly all this information could fall short of labeling transparent any opinion, restricted to the evaluative phase.…”