DNA Mixture Interpretations and Statistics – To Include or Exclude Cybergenetics © 2003-2013 Prescription for Criminal Justice Forensics ABA Criminal Justice.

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Presentation transcript:

DNA Mixture Interpretations and Statistics – To Include or Exclude Cybergenetics © Prescription for Criminal Justice Forensics ABA Criminal Justice Section New York, NY June, 2013 Mark W Perlin, PhD, MD, PhD Cybergenetics, Pittsburgh, PA

CHILD & CHILD & CHILD VICTIM Television Cabinet Table L-Shaped Couch Bathroom Bedroom Laundry Bedroom Stairs Bookcase VICTIM Storage Door to Outside Closet underpants pajama pants

DNA mixture data Quantitative peak heights at a locus peak size peak height

Peak thresholds Threshold Under threshold, don't use alleles Allele Pair 7, 7 7, 10 7, 12 7, 14 10, 10 0%10, 12 10, 14 12, 12 12, 14 14, 14 Simplify data for manual review

Allele dropout Threshold Under threshold, use alleles anyway Allele Pair 7, 7 7, 10 7, 12 7, 14 10, 10 > 0% 10, 12 10, 14 12, 12 12, 14 14, 14 Conjure phantom peaks

Manual interpretation issues Evidence call good data inconclusive peaks are too low for methods too many contributors to handle potential examination bias Database hit by association, not by match comparison: make false hits restrict upload: lose true hits

TrueAllele ® genotype model Evidence preserve data information use all peaks, high or low any number of contributors entirely objective, no bias Database hit based on LR match statistic sensitive: find true hits specific: only true hits

Mixture weight Separate mixture data into its contributor components 25%75%

Genotype inference Thorough: consider every possible genotype solution Objective: does not know the comparison genotype Explain the peak pattern Better explanation has a higher likelihood Victim's allele pair Another person's allele pair

Match information Probability(evidence match) Probability(coincidental match) How much more does the suspect match the evidence than a random person? 30x 3% 98%

TrueAllele inclusion Finds the right answer 11

Thresholds lose information Understate the probative force 26 Threshold Stochastic Threshold

TrueAllele exclusion Does not find the wrong answer – 20

TrueAllele usage child molester got: 20 quadrillion match, 22 years validation study: 4 peer-reviewed scientific papers admissibility: Pennsylvania, California, N. Ireland precedent: Pennsylvania appellate ruling approval: NYS Commission on Forensic Science cases: over 100 reports in criminal cases trials: over 15 (rape, murder, terror, weapons,...)

TrueAllele deployment Casework system Interpretation services

DNA truth, criminal justice This truth is incontrovertible. Panic may resent it, ignorance may deride it, malice may distort it, but there it is. - Winston Churchill Policeeffective database Prosecutor convict the guilty Defenderexonerate innocent Courtthe whole truth Citizenprevent crime Genotype models are more accurate. Who cares?

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