How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American...

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How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences American Academy of Forensic Sciences February, 2013 February, 2013 Washington, DC Washington, DC Mark W Perlin, PhD, MD, PhD Mark W Perlin, PhD, MD, PhD Kiersten Dormer, MS and Jennifer Hornyak, MS Kiersten Dormer, MS and Jennifer Hornyak, MS Cybergenetics, Pittsburgh, PA Cybergenetics, Pittsburgh, PA Thomas Meyers, MS and Walter Lorenz Thomas Meyers, MS and Walter Lorenz Allegheny County Medical Examiner’s Office, Pittsburgh, PA Allegheny County Medical Examiner’s Office, Pittsburgh, PA Cybergenetics © 2003-2013 Cybergenetics © 2003-2013

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Page 1: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

How Inclusion Interpretation of DNA Mixture Evidence Reduces

Identification Information

American Academy of Forensic SciencesAmerican Academy of Forensic SciencesFebruary, 2013February, 2013

Washington, DCWashington, DC

Mark W Perlin, PhD, MD, PhD Mark W Perlin, PhD, MD, PhD Kiersten Dormer, MS and Jennifer Hornyak, MSKiersten Dormer, MS and Jennifer Hornyak, MS

Cybergenetics, Pittsburgh, PACybergenetics, Pittsburgh, PAThomas Meyers, MS and Walter LorenzThomas Meyers, MS and Walter Lorenz

Allegheny County Medical Examiner’s Office, Pittsburgh, PA Allegheny County Medical Examiner’s Office, Pittsburgh, PA

Cybergenetics © 2003-2013Cybergenetics © 2003-2013

Page 2: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

DNA Mixture DataQuantitative peak heights at a locus

Allele value

Allele quantity

Page 3: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

Genotype InferenceComputer-based probabilistic genotyping

Explain thepeak pattern

Victim's allele pair

Another person's Another person's allele pairallele pair

Allele Pair5%15, 15

90%15, 165%15, 17

15, 1816, 1616, 1716, 1817, 1717, 1818, 18

Thorough & objective

Page 4: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

Identification InformationLikelihood Ratio

Explaining all the data under two competing hypotheses

Matchinggenotypeprobability

Evidence

Coincidence

90%

9%LR =

90%9%

= 10

log(LR) = log(10) = 1 ban

Page 5: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

Evidence Information

Perlin MW, Belrose JL, Duceman BW. New York State TrueAllele® Casework Validation Study. Journal of Forensic Sciences. 2013;58(6):in press.

log(LR)

Cou

nt

Identification information

13.69 (3.82)

Page 6: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

Data Summary for CPIOver threshold, peaks are labeled as allele events

All-or-none allele events

Threshold

Allele Pair5%15, 159%15, 16

15%15, 179%15, 185%16, 16

15%16, 179%16, 18

13%17, 1715%17, 18

5%18, 18

Page 7: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

Information Loss

Evidence

Coincidence

9%

9%LR =

9%9%

= 1

log(LR) = log(1) = 0 ban

Matchinggenotypeprobability

Combined probability of inclusion

CPI explains less of the data (no peak heights or model)

Page 8: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

Evidence CPI Statistic

Perlin MW, Belrose JL, Duceman BW. New York State TrueAllele® Casework Validation Study. Journal of Forensic Sciences. 2013;58(6):in press.

log(LR)

Cou

nt

Identification informationCPI match statistic

13.69 (3.82)

6.58 (0.80)

Page 9: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

Mixture Information Study

16 cases31 evidence items41 genotype matches

2 & 3 person DNA mixtures

Crimehomicide (7)sexual assault (5)assault (2)death investigation (1)robbery (1)

Itemclothing (12)weapon (6) vehicle (5)skin swab (3)vaginal swab (3)fingernail (1)rectal swab (1)

Page 10: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

Match Information vs. StatisticComputer-inferred genotype information (LR)Human review data summary statistic (CPI)

41 genotypes x 15 loci 615 locus experiments

517 drop out or imbalance?

human review?

29 68

YES NO

YES NO

Computer-only results

Computer & CPI

Page 11: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

Information (per locus)

log(LR)

Cou

nt

LR computer information(ban per locus)

0.746 (0.590)N = 517

Page 12: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

CPI Statistic (per locus)

log(LR)

Cou

nt

LR computer informationCPI human match statistic

0.000 (0.615)0.489

0.746 (0.590)N = 517

Page 13: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

Same Inform

ation

Conservative

Overstated

Imaginative

log(LR) information

log(

CP

I) s

tatis

tic

Joint Statistic Distribution

Page 14: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

Joint Statistic Distribution

rr2

= 0.376= 0.141

17.6%17.6%

10.1%10.1%

72.3%72.3%

log(LR) information

log(

CP

I) s

tatis

tic

Page 15: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

Computer-only Results

log(LR)

Cou

nt

YESNO

Free of drop-out or imbalance?

0.659 (0.664)N = 68

– 0.755 (0.346)N = 29

Page 16: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

Conclusions

• CPI does not correlate well with identification information• CPI acts like a random positive number generator• more loci give a higher statistic; not more information

• 28% of the time CPI overstates actual information• lower error with the major of a two person mixture

• time to move on … probabilistic genotyping and LR

CPI locus statistic relative to true information

Page 17: How Inclusion Interpretation of DNA Mixture Evidence Reduces Identification Information American Academy of Forensic Sciences February, 2013 Washington,

More information

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