### Abstract

Likelihood ratios are necessary to properly interpret mixed stain DNA evidence. They can flexibly consider alternate hypotheses and can account for population substructure. The likelihood ratio should be seen as an estimate and not a fixed value, because the calculations are functions of allelic frequency estimates that were estimated from a small portion of the population. Current methods do not account for uncertainty in the likelihood ratio estimates and are therefore an incomplete picture of the strength of the evidence. We propose the use of a confidence interval to report the consequent variation of likelihood ratios. The confidence interval is calculated using the standard forensic likelihood ratio formulae and a variance estimate derived using the Taylor expansion. The formula is explained, and a computer program has been made available. Numeric work shows that the evidential strength of DNA profiles decreases as the variation among populations increases.

Original language | English |
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Journal | Journal of Forensic Sciences |

Volume | 56 |

Issue number | SUPPL. 1 |

DOIs | |

State | Published - Jan 1 2011 |

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### Keywords

- Confidence intervals
- DNA typing
- Forensic science
- Likelihood ratios
- Mixed DNA profiles
- Population structure

### ASJC Scopus subject areas

- Pathology and Forensic Medicine
- Genetics

### Cite this

**Confidence Interval of the Likelihood Ratio Associated with Mixed Stain DNA Evidence.** / Beecham, Gary W; Weir, Bruce S.

Research output: Contribution to journal › Article

*Journal of Forensic Sciences*, vol. 56, no. SUPPL. 1. https://doi.org/10.1111/j.1556-4029.2010.01600.x

}

TY - JOUR

T1 - Confidence Interval of the Likelihood Ratio Associated with Mixed Stain DNA Evidence

AU - Beecham, Gary W

AU - Weir, Bruce S.

PY - 2011/1/1

Y1 - 2011/1/1

N2 - Likelihood ratios are necessary to properly interpret mixed stain DNA evidence. They can flexibly consider alternate hypotheses and can account for population substructure. The likelihood ratio should be seen as an estimate and not a fixed value, because the calculations are functions of allelic frequency estimates that were estimated from a small portion of the population. Current methods do not account for uncertainty in the likelihood ratio estimates and are therefore an incomplete picture of the strength of the evidence. We propose the use of a confidence interval to report the consequent variation of likelihood ratios. The confidence interval is calculated using the standard forensic likelihood ratio formulae and a variance estimate derived using the Taylor expansion. The formula is explained, and a computer program has been made available. Numeric work shows that the evidential strength of DNA profiles decreases as the variation among populations increases.

AB - Likelihood ratios are necessary to properly interpret mixed stain DNA evidence. They can flexibly consider alternate hypotheses and can account for population substructure. The likelihood ratio should be seen as an estimate and not a fixed value, because the calculations are functions of allelic frequency estimates that were estimated from a small portion of the population. Current methods do not account for uncertainty in the likelihood ratio estimates and are therefore an incomplete picture of the strength of the evidence. We propose the use of a confidence interval to report the consequent variation of likelihood ratios. The confidence interval is calculated using the standard forensic likelihood ratio formulae and a variance estimate derived using the Taylor expansion. The formula is explained, and a computer program has been made available. Numeric work shows that the evidential strength of DNA profiles decreases as the variation among populations increases.

KW - Confidence intervals

KW - DNA typing

KW - Forensic science

KW - Likelihood ratios

KW - Mixed DNA profiles

KW - Population structure

UR - http://www.scopus.com/inward/record.url?scp=78650747892&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=78650747892&partnerID=8YFLogxK

U2 - 10.1111/j.1556-4029.2010.01600.x

DO - 10.1111/j.1556-4029.2010.01600.x

M3 - Article

C2 - 21198611

AN - SCOPUS:78650747892

VL - 56

JO - Journal of Forensic Sciences

JF - Journal of Forensic Sciences

SN - 0022-1198

IS - SUPPL. 1

ER -