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Objective DNA Mixture Information in the Courtroom: Relevance, Reliability and Acceptance

Perlin, M.W. Objective DNA mixture information in the courtroom: relevance, reliability and acceptance. Presented at the International Symposium on Forensic Science Error Management: Detection, Measurement and Mitigation, National Institute of Standards and Technology. Arlington, VA, 2015.




DNA mixtures arise when two or more people contribute their DNA to a biological sample. Data-simplifying thresholds fail to give accurate results when applied to complex mixture patterns. An entirely objective interpretation approach is to first separate out the genotypes of each mixture contributor, without ever seeing the subject, and only afterwards make a comparison.

Comparison of a separated evidence genotype with a subject's reference genotype, relative to a population, yields a match statistic. This likelihood ratio is a standard measure of information change based on observed evidence that addresses FRE 403 relevancy balancing. The reliability of objective genotype separation has been extensively tested. Such extensive testing, error rate determination, and scientific peer-review address FRE 702 and Daubert reliability factors.

Courts have accepted this extensively validated computer approach, with admissibility upheld at the appellate level. Separated genotypes provide results that juries find easy to understand. Objective DNA analysis elicits identification information from evidence, while rigorous validation establishes accuracy and error rates. Courts require solid science - extensively tested and empirically proven - to promote criminal justice, societal safety, and conviction integrity.