Performance of a method for weighting a range in the number of contributors in probabilistic genotyping

•Optimal parameters defined for the variable number of contributors (varNoC) method.•varNoC LR stable when number of contributors range under- or over-assigned.•Variability in Pr(Nn|O) is linked to under-assignment in contributors range. Uncertainty in the assignment of the number of contributors (N...

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Veröffentlicht in:Forensic science international : genetics 2020-09, Vol.48, p.102352-102352, Article 102352
Hauptverfasser: McGovern, Catherine, Cheng, Kevin, Kelly, Hannah, Ciecko, Anne, Taylor, Duncan, Buckleton, John S., Bright, Jo-Anne
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Sprache:eng
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Zusammenfassung:•Optimal parameters defined for the variable number of contributors (varNoC) method.•varNoC LR stable when number of contributors range under- or over-assigned.•Variability in Pr(Nn|O) is linked to under-assignment in contributors range. Uncertainty in the assignment of the number of contributors (NoC) can be encountered, particularly in higher-order mixtures, where alleles may be shared between contributors, may have dropped out, or may be masked by the stutter artefacts or allelic peaks of a more dominant contributor. Most probabilistic genotyping software requires the assignment of NoC prior to interpretation. NoC has been described as a nuisance parameter. Taylor et al. [1] describe a method to weigh the probability of the profile under different values of N and incorporate this into a likelihood ratio (LR). Within this paper we explore the performance of this variable number of contributors (varNoC) method programmed within the probabilistic genotyping software STRmix™. The desired combination of performance and runtime was obtained using the default STRmix™ version 2.7 MCMC settings in conjunction with a 2.5 % hyper-rectangle range, at least 10,000 naïve MC iterations and 8 MCMC chains. The varNoC LR demonstrated the typical sensitivity and specificity behaviour seen in previous studies, with a high level of reproducibility given repeat analyses. Profiles previously demonstrating ambiguity in the NoC assigned using conventional estimation methods, were able to be reliably interpreted and a varNoC LR assigned.
ISSN:1872-4973
1878-0326
DOI:10.1016/j.fsigen.2020.102352