finding truth in dna mixture evidence innocence network conference april, 2013 charlotte, nc mark w...
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Finding Truth in DNA Mixture Evidence
Innocence Network ConferenceInnocence Network ConferenceApril, 2013April, 2013
Charlotte, NCCharlotte, NC
Mark W Perlin, PhD, MD, PhD Mark W Perlin, PhD, MD, PhD Cybergenetics, Pittsburgh, PACybergenetics, Pittsburgh, PA
Cybergenetics © 2003-2013Cybergenetics © 2003-2013
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DNA Mixture DataQuantitative peak heights at a locus
peak size
peakheight
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Peak Thresholds
Threshold
Under threshold, don't use alleles
Allele Pair7, 77, 107, 127, 14
10, 100%10, 12
10, 1412, 1212, 1414, 14
Simplify data for human review
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Allele Dropout
Threshold
Under threshold, use alleles anyway
Allele Pair7, 77, 107, 127, 14
10, 10> 0% 10, 12
10, 1412, 1212, 1414, 14
Conjure phantom peaks
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Human Interpretation Issues
Evidence• call good data inconclusive• peaks are too low for them• too many contributors to handle• potential examination bias
Database• hit by association, not by match• comparison: make false hits• restrict upload: lose true hits
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TrueAllele® Casework
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
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Validation Studies
Perlin MW, Sinelnikov A. An information gap in DNA evidence interpretation. PLoS ONE. 2009;4(12):e8327.
Perlin MW, Legler MM, Spencer CE, Smith JL, Allan WP, Belrose JL, Duceman BW. Validating TrueAllele® DNA mixture interpretation. Journal of Forensic Sciences. 2011;56(6):1430-47.
Perlin MW, Belrose JL, Duceman BW. New York State TrueAllele® Casework validation study. Journal of Forensic Sciences. 2013;58(6):in press.
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Separate Mixture Contributors
25% 75%
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GenotypeThorough: consider every possible genotype solutionObjective: does not know the comparison genotype
Explain thepeak pattern
Betterexplanationhas ahigher likelihood
Victim's allele pair
Another person's Another person's allele pairallele pair
Allele Pair7, 77, 107, 127, 14
10, 1098%10, 12
10, 1412, 1212, 1414, 14
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Handgun @ locus TH01Three person mixtureLab says: inconclusive
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TrueAllele mixture interpretationGenotype probability distributionThorough & objective
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Handgun does NOT match suspectComputer statistic AGAINST match
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Informative TrueAllele genotypeExpected match statistic: million/billionSearch a DNA database for the right man?
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The Search for Truth
M. W. Perlin, "When good DNA goes bad," Journal of Forensic Research, S11:003, 2013.
M. W. Perlin, "DNA Identification Science," in Forensic Sciences, volume 3. C. H. Wecht, Ed., Albany, NY: LexisNexis Matthew Bender, Chapter 37C, 2012.
M. W. Perlin. "Forensic science in the information age." Forensic Magazine, 9(2):17-21, 2012.
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More information
http://www.cybgen.com/information• Courses• Newsletters• Newsroom• Presentations• Publications