new york state police trueallele ® casework developmental validation cybergenetics © 2003-2010 new...
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New York State PoliceTrueAllele® Casework
Developmental Validation
Cybergenetics © 2003-2010Cybergenetics © 2003-2010
New York State DNA SubcommitteeNew York State DNA SubcommitteeMarch, 2010March, 2010
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Information Gain (LR)identification hypothesis:
the suspect contributed to the evidence
information gain(likelihood ratio)
Odds(hypothesis | data)
Odds(hypothesis)before
after
= data
Additive information units: log(LR)Order of magnitude, powers of ten
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DNA Mixture Data
Some amount of contributor A
genotype
Other amount of contributor B
genotype
Mixture data withgenotypes of
contributors A & B
+ PCR
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Quantitative Mixture InterpretationStep 1: infer genotype
• consider every possible allele pair• compare pattern with DNA data• Rule: better fit's more likely it
high likelihood
low likelihood
?
?
genotype
a,ba,cb,dc,d…
allele pair probability
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Information Gain (LR)Step 2: match genotypes
At the suspect's genotype allele pair,what is the locus information gain?
information gain(likelihood ratio)
Prob(allele pair | data)
Prob(allele pair)before
after
= data
Computer objectivity: (Step 1) infer evidence genotype from data
(Step 2) compare genotype with suspect
(population)
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Qualitative Manual ReviewStep 1: infer genotype
Rule: every pair gets equal share
listed allele pairsare all assigned
the same likelihood
?
?
genotype
a,aa,ba,ca,d…
allele pair likelihood
Step 2: match genotype
lower probability means lower information gain (LR)
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Comparisontwo unknown
(without victim)one unknown(with victim)
quantitativecomputer
qualitativehuman
improvement
13.2613.26 (0.175)(0.175)(ten trillion)(ten trillion)
7.037.03(ten million)(ten million)
6.246.24(one million)(one million)
17.3317.33 (0.036)(0.036)(hundred quadrillion)(hundred quadrillion)
12.6612.66(fifty trillion)(fifty trillion)
4.674.67(fifty thousand)(fifty thousand)
interpretationmethod
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Summary
• information gain (LR) is a universal DNA metric• efficacy: computer extracts useful information• improvement: computer mixture interpretation is more informative than human review with victim 50,000x - without victim 1,000,000x• reproducibility: tenths of a log(LR) unit• objectivity: "parallel unmasking", infer then match• productivity: lab gives statistic for 1 of 3 items • utility: science, investigation and evidence
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Commonwealth vs. Foley
Apr 2006: Blairsville Dentist John Yelenic murdered
Nov 2007: Trooper Kevin Foley charged with crime
Feb 2008: Defense questions 13,000 DNA match score
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DNA Evidence
• DNA from under victim's fingernails (Q83)• two contributors to DNA mixture• 93.3% victim & 6.7% unknown• 1,000 pg DNA in 25 ul• STR analysis with ProfilerPlus®, Cofiler® • know victim contributor genotype (K53) • TrueAllele® computer interpretation (using genotype addition method) infer unknown contributor genotype • only after having inferred unknown, compare with suspect genotype (K2)
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Three DNA Match Statistics
Score Method13 thousand inclusion
23 million subtraction189 billion addition
• Why are there different match results?• How do mixture interpretation methods differ?• What should we present in court?
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Different Interpretation Methods
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Frye: General Acceptance in the Relevant Community
• Quantitative STR Peak Information• Genotype Probability Distributions• Computer Interpretation of STR Data• Statistical Modeling and Computation• Likelihood Ratio Literature• Mixture Interpretation Admissibility• Computer Systems for Quantitative DNA Mixture Deconvolution• TrueAllele Casework Publications
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Expected Result
15 loci
12 loci
67
Perlin MW, Sinelnikov A. An information gap in DNA evidence
interpretation. PLoS ONE. 2009;4(12):e8327.
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Expert Testimony
Dr. Perlin explained to the jury why these apparently different results were expected by DNA science. "The less informative methods ignored some of the data," said Dr. Perlin, "while the TrueAllele computation considered all of the available DNA data."
"A scientist may look at the same slide using the naked eye, a magnifying glass, or a microscope," analogized Dr. Perlin. "A computer that considers all the data is a more powerful DNA microscope."
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Mixture Weight
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Inferred Genotype
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log(LR) Match Information
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Locus D8S1179 Data
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Explain D8S1179 Genotype
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Likelihood Comparison
better fit's more likely itbetter fit's more likely it
every pair gets equal shareevery pair gets equal share
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Generate Report
Locus information gain is genotypeprobability ratio:LR = after/before
Joint informationis the sum of thelocus information
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Case Observations
• objective review never saw suspect• easy to testify about in court• understandable to judge and jury• have precedent: admitted, testified• preserve match information in data• rapid response to attorney• multiple match scores presented all information to the triers of fact – nothing was withheld from the jury this should be standard practice
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One Verdict
"John Yelenic provided the most eloquent and poignant evidence in this case," said the prosecutor, senior deputy attorney general Anthony Krastek. "He managed to reach out and scratch his assailant," capturing the murderer's DNA under his fingernails.
The DNA Investigator Newsletter. Same Data, More Information - Murder, Match and DNA, Cybergenetics, 2009.
www.cybgen.com/information/newsletters/CybgenNews1.pdf
One Verdict
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Three Unknown Contributors
12% 27% 60%
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17.7 11.6 11.3
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ProductivityTrueAllele
log(LR)information
human reviewmatch scoresuccess rate
simpleN = 35
intermediateN = 20
complexN = 33
16.316.3(ten quadrillion)(ten quadrillion)
13.113.1(ten trillion)(ten trillion)
11.911.9(one trillion)(one trillion)
49%49%
25%25%
21%21%
caseclassification
0.100.10
0.260.26
0.440.44
log(LR)standarddeviation