# When evaluating DNA evidence within a likelihood ratio framework, should the propositions be exhaustive?

## Détails

ID Serval

serval:BIB_00973C41BA2C

Type

**Article**: article d'un périodique ou d'un magazine.

Collection

Publications

Institution

Titre

When evaluating DNA evidence within a likelihood ratio framework, should the propositions be exhaustive?

Périodique

Forensic science international. Genetics

ISSN

1878-0326 (Electronic)

ISSN-L

1872-4973

Statut éditorial

Publié

Date de publication

01/2021

Peer-reviewed

Oui

Volume

50

Pages

102406

Langue

anglais

Notes

Publication types: Journal Article

Publication Status: ppublish

Publication Status: ppublish

Résumé

We seek to develop a rational approach to forming propositions when little information is available from the outset, as this often happens in casework. If propositions used when evaluating evidence are not exhaustive (in the context of the case), then there is a theoretical risk that an LR greater than one may be associated with a proposition in the numerator that - if all meaningful propositions had been considered - would in fact have a lower posterior probability after consideration of the evidence. Ideally, all propositions should be considered. However, with multiple propositions, some terms will be larger than others and for simplification very small terms can be neglected without changing the order of magnitude of the value of the evidence (i.e. LR). Our analysis shows that mathematically a contributor's DNA can be assumed to be present under both prosecution and alternative propositions (H <sub>p</sub> and H <sub>a</sub> ) if there is a reasonable prior probability of their DNA being present and their inclusion is supported by the profile. This is because the terms associated to these sub-propositions will dominate our LR. For example, in the absence of specific information, when considering two persons of interest (POI) as potential contributors to a mixed DNA profile we suggest the assumption of one when examining the presence of the other, after checking that both collectively explain the profile well. This represents more meaningful propositions and allows better discrimination. Slooten and Caliebe have shown that the overall LR is the weighted average of LRs with the same number of contributors (NoC) under both propositions. The weights involve both an assessment of the probability of the crime scene DNA profile and the probability of this NoC given the background information.

Mots-clé

Forensic DNA, exhaustive, likelihood ratio, propositions

Pubmed

Création de la notice

04/11/2020 15:39

Dernière modification de la notice

20/03/2021 7:26