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General random match probability for DNA mixtures
With simple DNA evidence, there is only one genotype possibility. Random match probability (RMP) tells us the chance of making a mistake. RMP gives the probability that someone unrelated to the defendant matches the DNA. The strength of evidence, or likelihood ratio (LR), is one over the RMP.
But with complex DNA, such as mixtures of two or more people, LR error becomes more complicated. More generally, the RMP is the chance that DNA evidence implicates an innocent person at least as strongly as it does the defendant. Finding the RMP may entail calculating LR values for a trillion trillion possibilities.
"The LR is the strength of forensic evidence, while RMP is the chance of making a mistake," says Dr. Mark Perlin of Cybergenetics. "Jurors can use error probability in assessing reasonable doubt." The TrueAllele® VUIer™ interface instantly calculates RMP error for probabilistic genotypes derived from DNA mixtures.
Dr. Perlin spoke about generalized RMP for DNA mixtures last week in Minneapolis at the 10th International Conference on Forensic Inference and Statistics (ICFIS). His half hour conceptual talk is accessible to lawyers and scientists. The webpage shows the YouTube presentation and has more information, including a technical report.
- Forensic match information: exact calculation and applications - Cybergenetics