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Pairwise relatedness testing in the context of inbreeding: expectation and variance of the likelihood ratio

In this paper we investigate various effects of inbreeding on the likelihood ratio (LR) in forensic kinship testing. The basic setup of such testing involves formulating two competing hypotheses, in the form of pedigrees, describing the relationship between the individuals. The likelihood of each hy...

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Autores principales: Brustad, Hilde Kjelgaard, Vigeland, Magnus Dehli, Egeland, Thore
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Springer Berlin Heidelberg 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7782430/
https://www.ncbi.nlm.nih.gov/pubmed/32989564
http://dx.doi.org/10.1007/s00414-020-02426-6
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author Brustad, Hilde Kjelgaard
Vigeland, Magnus Dehli
Egeland, Thore
author_facet Brustad, Hilde Kjelgaard
Vigeland, Magnus Dehli
Egeland, Thore
author_sort Brustad, Hilde Kjelgaard
collection PubMed
description In this paper we investigate various effects of inbreeding on the likelihood ratio (LR) in forensic kinship testing. The basic setup of such testing involves formulating two competing hypotheses, in the form of pedigrees, describing the relationship between the individuals. The likelihood of each hypothesis is computed given the available genetic data, and a conclusion is reached if the ratio of these exceeds some pre-determined threshold. An important aspect of this approach is that the hypotheses are usually not exhaustive: The true relationship may differ from both of the stated pedigrees. It is well known that this may introduce bias in the test results. Previous work has established formulas for the expected value and variance of the LR, given the two competing hypotheses and the true relationship. However, the proposed method only handles cases without inbreeding. In this paper we extend these results to all possible pairwise relationships. The key ingredient is formulating the hypotheses in terms of Jacquard coefficients instead of the more restricted Cotterman coefficients. While the latter describe the relatedness between outbred individuals, the more general Jacquard coefficients allow any level of inbreeding. Our approach also enables scrutiny of another frequently overlooked source of LR bias, namely background inbreeding. This ubiquitous phenomenon is usually ignored in forensic kinship computations, due to lack of adequate methods and software. By leveraging recent work on pedigrees with inbred founders, we show how background inbreeding can be modeled as a continuous variable, providing easy-to-interpret results in specific cases. For example, we show that if true siblings are subjected to a test for parent-offspring, moderate levels of background inbreeding are expected to inflate the LR by more than 50%.
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spelling pubmed-77824302021-01-11 Pairwise relatedness testing in the context of inbreeding: expectation and variance of the likelihood ratio Brustad, Hilde Kjelgaard Vigeland, Magnus Dehli Egeland, Thore Int J Legal Med Original Article In this paper we investigate various effects of inbreeding on the likelihood ratio (LR) in forensic kinship testing. The basic setup of such testing involves formulating two competing hypotheses, in the form of pedigrees, describing the relationship between the individuals. The likelihood of each hypothesis is computed given the available genetic data, and a conclusion is reached if the ratio of these exceeds some pre-determined threshold. An important aspect of this approach is that the hypotheses are usually not exhaustive: The true relationship may differ from both of the stated pedigrees. It is well known that this may introduce bias in the test results. Previous work has established formulas for the expected value and variance of the LR, given the two competing hypotheses and the true relationship. However, the proposed method only handles cases without inbreeding. In this paper we extend these results to all possible pairwise relationships. The key ingredient is formulating the hypotheses in terms of Jacquard coefficients instead of the more restricted Cotterman coefficients. While the latter describe the relatedness between outbred individuals, the more general Jacquard coefficients allow any level of inbreeding. Our approach also enables scrutiny of another frequently overlooked source of LR bias, namely background inbreeding. This ubiquitous phenomenon is usually ignored in forensic kinship computations, due to lack of adequate methods and software. By leveraging recent work on pedigrees with inbred founders, we show how background inbreeding can be modeled as a continuous variable, providing easy-to-interpret results in specific cases. For example, we show that if true siblings are subjected to a test for parent-offspring, moderate levels of background inbreeding are expected to inflate the LR by more than 50%. Springer Berlin Heidelberg 2020-09-28 2021 /pmc/articles/PMC7782430/ /pubmed/32989564 http://dx.doi.org/10.1007/s00414-020-02426-6 Text en © The Author(s) 2020 Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
spellingShingle Original Article
Brustad, Hilde Kjelgaard
Vigeland, Magnus Dehli
Egeland, Thore
Pairwise relatedness testing in the context of inbreeding: expectation and variance of the likelihood ratio
title Pairwise relatedness testing in the context of inbreeding: expectation and variance of the likelihood ratio
title_full Pairwise relatedness testing in the context of inbreeding: expectation and variance of the likelihood ratio
title_fullStr Pairwise relatedness testing in the context of inbreeding: expectation and variance of the likelihood ratio
title_full_unstemmed Pairwise relatedness testing in the context of inbreeding: expectation and variance of the likelihood ratio
title_short Pairwise relatedness testing in the context of inbreeding: expectation and variance of the likelihood ratio
title_sort pairwise relatedness testing in the context of inbreeding: expectation and variance of the likelihood ratio
topic Original Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7782430/
https://www.ncbi.nlm.nih.gov/pubmed/32989564
http://dx.doi.org/10.1007/s00414-020-02426-6
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