In 2015 and 2016 the Central Unit of the Dutch National Police created and submitted 21 cartridge case comparison tests as real cases to the Netherlands Forensic Institute (NFI), under supervision... Show moreIn 2015 and 2016 the Central Unit of the Dutch National Police created and submitted 21 cartridge case comparison tests as real cases to the Netherlands Forensic Institute (NFI), under supervision of the University of Twente (UT). A total of 53 conclusions were drawn in these 21 tests. For 31 conclusions the underlying ground truth was ‘positive’, in the sense that it addressed a cluster of cartridge cases that was fired from the same firearm. For 22 conclusions the ground truth was ‘negative’, in the sense that the cartridge cases were fired from different firearms. In none of the conclusions, resulting from examinations under casework conditions, misleading evidence was reported. All conclusions supported the hypothesis reflecting the ground truth. This article discusses the design and results of the tests in more detail. Show less
We would like to respond to the recent paper “Understanding forensic expert evaluative evidence: A study of the perception of verbal expressions of the strength of evidence”, by Arscott et al.. We... Show moreWe would like to respond to the recent paper “Understanding forensic expert evaluative evidence: A study of the perception of verbal expressions of the strength of evidence”, by Arscott et al.. We agree that a verbal expression of the strength of evidence can be interpreted in varying ways. Not only by the people that read them, but also by those that express them. It is also possible that different verbal expressions are interpreted in the same way by different readers or reporting scientists. This is the reason that the Association of Forensic Science Providers (AFSP) and the European Network of Forensic Science Institutes (ENFSI) have published guidelines that call for forensic institutes to provide verbal scales and numerically define the verbal expressions therein. This, at least formally, solves the issue of the perception of intended strength of evidence. Show less
In this response paper, part of the Virtual Special Issue on “Measuring and Reporting the Precision of Forensic Likelihood Ratios”, we further develop our position on likelihood ratios which we... Show moreIn this response paper, part of the Virtual Special Issue on “Measuring and Reporting the Precision of Forensic Likelihood Ratios”, we further develop our position on likelihood ratios which we described previously in Berger et al. (2016) “The LR does not exist”. Our exposition is inspired by an example given in Martire et al. (2016) “On the likelihood of encapsulating all uncertainty”, where the consequences of obtaining additional information on the LR were discussed. In their example, two experts use the same data in a different way, and the LRs of these experts change differently when new data are taken into account. Using this example as a starting point we will demonstrate that the probability distribution for the frequency of the characteristic observed in trace and reference material can be used to predict how much an LR will change when new data become available. This distribution can thus be useful for such a sensitivity analysis, and address the question of whether to obtain additional data or not. But it does not change the answer to the original question of how to update one’s prior odds based on the evidence, and it does not represent an uncertainty on the likelihood ratio based on the current data. Show less
