Citation

Slooten K, Berger CEH. Sci. Justice 2017; 57(6): 468-471.

Affiliation

Netherlands Forensic Institute, P.O. Box 24044, 2490 AA The Hague, The Netherlands; Leiden University, Institute for Criminal Law and Criminology, P.O. Box 9520, 2300 RA Leiden, The Netherlands.

Copyright

(Copyright © 2017, Forensic Science Society, Publisher Elsevier Publishing)

DOI

10.1016/j.scijus.2017.05.007

PMID

29173461

Abstract

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 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.

Copyright © 2017 The Chartered Society of Forensic Sciences. Published by Elsevier B.V. All rights reserved.

Language: en

Keywords

Evidence interpretation; Likelihood ratio; Subjective probability