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

DNA Mixture Interpretations and Statistics –

To Include or Exclude

Cybergenetics © 2003-2013Cybergenetics © 2003-2013

Prescription for Criminal Justice ForensicsABA Criminal Justice Section

New York, NYNew York, NYJune, 2013June, 2013

Mark W Perlin, PhD, MD, PhDMark W Perlin, PhD, MD, PhDCybergenetics, Pittsburgh, PACybergenetics, Pittsburgh, PA

CHILD&

CHILD

CHILD&

CHILDCHILD

VICTIM

Television

Cabinet

Table

Table

L-Shaped Couch

Bathroom

Bed

room

Lau

ndry

Bed

room

StairsBookcase

VICTIM

VICTIM

Storage

Door to OutsideCloset

underpants

pajama pants

DNA mixture dataQuantitative peak heights at a locus

peak size

peakheight

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 manual review

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

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 weightSeparate mixture data into its contributor components

25% 75%

Genotype inferenceThorough: 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

Match information

Probability(evidence match)

Probability(coincidental match)

How much more does the suspect match the evidencethan a random person?

30x

3%

98%

TrueAllele inclusionFinds the right answer

11

Thresholds lose informationUnderstate the probative force

2 6

ThresholdStochastic Threshold

TrueAllele exclusionDoes 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 systemInterpretation services

DNA truth, criminal justiceThis truth is incontrovertible. Panic may resent it, ignorance may deride it, malice may distort it, but there it is. - Winston Churchill

Police effective databaseProsecutor convict the guiltyDefender exonerate innocentCourt the whole truthCitizen prevent crime

Genotype models are more accurate. Who cares?

More information

perlin@cybgen.com

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