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WIREs Forensic Sci

Bayesian networks for the interpretation of biological evidence

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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
Examples of questions that could be asked at every level in the “hierarchy of propositions”
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Example of a Bayesian network with three nodes A, B, and C with their associated probability tables. Note: This example has “0.5” for every probability; in a real case, probabilities would be based on experimental data or observations
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