Interpreting DNA Mixtures

Abstract

The interpretation of mixed DNA stains is explained in the context of likelihood ratios. The probabilities for the mixedstain profile are evaluated under alternative explanations that specify the numbers of contributors and the profiles of any known contributors. Interpretations based simply on the frequencies with which random members of a population would not be excluded from a mixed-stain profile do not make use of all the information, and may overstate the strength of the evidence against included people. The effects of the numbers of contributors depends on whether all the alleles at a locus are present in the mixed stain. A general equation is given to allow likelihood ratios to be calculated, and includes the "2p" modification suggested by the 1996 NRC report. This modification is not always conservative. A computer program to perform calculations is available.

Trace samples of human blood in mosquitoes as a forensic investigation tool

“…Genetic analysis and interpretation of this kind of criminal evidence is assisted by statistical analysis using the LR (Weir et al, 1997;Hu et al, 2003;González-Andrade et al, 2006;Primorac and Schanfield, 2014), which is the probability of association between possible trace samples (human blood found in the digestive tract of mosquitoes) and references samples. González-Andrade et al (2006), who reviewed cases of sex offenders and the resulting mixture genetic profiles, the calculation result of LR was one million, whereas the analysis of human blood hematophagous mosquitoes found in the lowest rate was LR approximately eight quintillion on a population; discriminating enough the association between the possible trace and reference samples.…”

DNA Identification of Biological Traces on Cigarettes: Vices Reveal

“…calculation of the likelihood ratio (lR) or Bayesian factor was used for representativeness of the established evidence sample (33). the likelihood ratio is explicit evidence for the probability to determine a given DNA profile if the cell material has been left by another person apart from suspect one or the perpetrator (9,12).…”

Statistical Analysis of Forensic Dna: Computational Problems Solved and to Be Solved

“…In fact, the NRC-I (1992) demonstrated the evaluation of a simple mixture problem, but the calculation was incorrect. Recently, Weir et al (1997) obtained a general formula, based on the generalization of results developed for simple cases, for the match probabilities in the mixture. The above work has been referred to for a fuller evaluation of mixed samples by the NRC-II (1996).…”

“…The above work has been referred to for a fuller evaluation of mixed samples by the NRC-II (1996). Evett et al (1991) and Weir et al (1997) employed the product rule in the mixed sample problem which required the assumption of HW equilibrium. As mentioned earlier, the HW law is seldom exactly certain or correct.…”