Since the interpretation of forensic evidence for source-level identification occurs within the context of two competing propositions for how the evidence has arisen, this article introduces two frameworks for quantifying the value of evidence in identification of source problems which formally and explicitly state the propositions based on sampling distributions.
The first is referred to as the identification of common source problems and focuses on providing evidentiary support for deciding whether two sets of unknown source evidence can be attributed to a common, but unknown, origin in a relevant background population. The second is referred to as the identification of specific source problem, and focuses on providing evidentiary support for deciding whether a single set of unknown source evidence can be attributed to a known, specified source or whether it originates from a source in the relevant background population. The motivations for this work came from recent calls for greater transparency and rigor in reporting evidential value, especially from the European Network of Forensic Science Institutes (ENFSI) guidelines, President's Council of Advisors on Science and Technology (PCAST), and the Department of Justice's review of the testimony of forensic examiners. As a working example, the article considers a debate that occurred during the recent NIST Colloquium on the Weight of Evidence. (publisher abstract modified)
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