Interpreting forensic DNA mixtures: allowing for uncertainty in population substructure and dependence

Summary. We consider the assessment of deoxyribonucleic acid (DNA) profiles from biological samples containing a mixture of DNA from more than one person. The problem has been investigated in the context of likelihood ratios by Weir and co-workers under the assumption of independent alleles in DNA profiles. However, uncertainty about independence may arise from various factors such as population substructure and relatedness. This issue has received considerable attention in recent years. Ignoring this uncertainty may seriously overstate the strength of the evidence and therefore disadvantage innocent suspects. Taking this uncertainty into account, we develop a general formula for calculating the match probabilities of DNA profiles. Thus, we extend the result derived by Weir and co-workers to the dependence situation, which is often more to the benefit of the defendant in comparison with the simple product rule result based on an independence assumption. The effect of dependence of alleles on likelihood ratio estimates can be seen in the analysis of two real data sets.

[1]  S WRIGHT,et al.  Genetical structure of populations. , 1950, Nature.

[2]  N E Morton,et al.  Genetic structure of forensic populations. , 1992, American journal of human genetics.

[3]  Ian W. Evett,et al.  Bayesian Analysis of DNA Profiling Data in Forensic Identification Applications , 1997 .

[4]  Are convenience DNA samples significantly different? , 1996, Forensic science international.

[5]  E. Buse,et al.  The effect of sampling error and measurement error and its correlation on the estimation of multi-locus fixed-bin VNTR RFLP genotype probabilities. , 1997, Journal of forensic sciences.

[6]  David J. Balding,et al.  Estimating Products in Forensic Identification Using DNA Profiles , 1995 .

[7]  B S Weir,et al.  Independence of VNTR alleles defined as fixed bins. , 1992, Genetics.

[8]  A. Jeffreys,et al.  Individual-specific ‘fingerprints’ of human DNA , 1985, Nature.

[9]  D. Lindley.  The 1988 Wald Memorial Lectures: The Present Position in Bayesian Statistics , 1990 .

[10]  The effect of ethnic and racial population substructuring on the estimation of multi-locus fixed-bin VNTR RFLP genotype probabilities. , 1997, Journal of forensic sciences.

[11]  J S Buckleton,et al.  Applications and extensions of subpopulation theory: a caseworkers guide. , 1998, Science & justice : journal of the Forensic Science Society.

[12]  S. Geisser,et al.  Testing Hardy-Weinberg equilibrium on allelic data from VNTR loci. , 1992, American Journal of Human Genetics.

[13]  A. P. Dawid,et al.  Coherent Analysis of Forensic Identification Evidence , 1996 .

[14]  K. Roeder.  DNA Fingerprinting: A Review of the Controversy , 1994 .

[15]  B. Weir,et al.  Interpreting DNA mixtures. , 1997, Journal of forensic sciences.

[16]  Colin Aitken,et al.  The use of statistics in forensic science , 1991 .

[17]  I W Evett,et al.  A guide to interpreting single locus profiles of DNA mixtures in forensic cases. , 1991, Journal - Forensic Science Society.

[18]  J A Lambert,et al.  Taking account of peak areas when interpreting mixed DNA profiles. , 1998, Journal of forensic sciences.

[19]  D J Balding,et al.  DNA profile match probability calculation: how to allow for population stratification, relatedness, database selection and single bands. , 1994, Forensic science international.