expert systems for automated str analysis swgdam quantico, va mark w. perlin january, 2003
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Expert Systems forExpert Systems forAutomated STR AnalysisAutomated STR Analysis
SWGDAMSWGDAMQuantico, VAQuantico, VA
Mark W. PerlinMark W. PerlinJanuary, 2003January, 2003
DNA Is Clue to 1971 Murder: A recent, random test links a state prison inmate to the old El Dorado case. January 10, 2003
DNA Clue Cracks Open Unsolved 1979 Slaying: Colorado felon charged in San Pablo girl's death. December 4, 2002
S.F. Transient Held in Rapes of Homeless Women: DNA match led to suspect. October 19, 2002
DNA links felon to rape: The arrest marks the 100th match in state database. August 23, 2002
DNA links parolee to old rape case: Database helps authorities score 'cold hit' on suspect in attack. August 21, 2002
DNA yields arrest warrant in 1978 killing. August 14, 2002
The analyst will simply submit the items for DNA analysis, using the final data interpretation step to determine relevance to the ongoing investigation ... The bottleneck becomes the interpretation of analytical results and the technical review process. ... Although these processes are currently dependent upon manual applications, software solutions are emerging that can be integrated into an automated approach.
Collect Crime Scene EvidenceCollect Crime Scene Evidence
Generate DNA DataGenerate DNA Data
Review DataReview Data
Present Results to Legal SystemPresent Results to Legal System
Collect Crime Scene EvidenceCollect Crime Scene Evidence
Generate DNA DataGenerate DNA Data
Review DNA DataReview DNA Data
Present Results to Legal SystemPresent Results to Legal System
TrueAllele™TrueAllele™
datadata
data peaksdata peakssize + [DNA]size + [DNA]
modelmodel
1. Input data
2. Q/C gel run
3. Call alleles
4. Output result
FSS ABI/377 ValidationFSS ABI/377 ValidationResourcesResources• • Data: 22,000 genotypes (SGMplus)Data: 22,000 genotypes (SGMplus)• • People: 6 reviewers + 6 managers People: 6 reviewers + 6 managers • • Time: 8 weeks work + 4 weeks reportTime: 8 weeks work + 4 weeks report
ComponentsComponents• • Peak height correlation (GS vs TA)Peak height correlation (GS vs TA)• • Establish baseline height (error-free)Establish baseline height (error-free)• • Designation accuracy (human vs TA)Designation accuracy (human vs TA)• • Network/computer environmentNetwork/computer environment• • QMS documentationQMS documentation
ResultsResults• • Greater yield with TAGreater yield with TA• • No errors on quality dataNo errors on quality data
denialdenial
angeranger
bargainingbargaining
depressiondepression
acceptanceacceptance
Generate STR DataGenerate STR Data
UK National DNA DatabaseUK National DNA Database
Person reviewsPerson reviewsa fractiona fraction
of the dataof the data
TrueAllele expert systemTrueAllele expert systemscores all STR data and scores all STR data and assesses data qualityassesses data quality
Validation MethodValidation Method
1. Obtain original data1. Obtain original data2. Process data in TrueAllele™ ES2. Process data in TrueAllele™ ES (auto-setup, process run, Q/A, (auto-setup, process run, Q/A, call alleles, apply rules, check)call alleles, apply rules, check) computer: accept/reject/editcomputer: accept/reject/edit3. Review all data3. Review all data one person, many computersone person, many computers human: accept/reject/edithuman: accept/reject/edit4. Generate results & stats4. Generate results & stats
Validation ResultsValidation Results
Computer: ~85% data, no review needed Computer: ~85% data, no review needed Human: Designations are correctHuman: Designations are correct
TrueAllele expert system can eliminateTrueAllele expert system can eliminatemost human review of STR DNA datamost human review of STR DNA data
JustAllele™JustAllele™
Genotype ProbabilityGenotype ProbabilitySample @ D7S820Sample @ D7S820
Option 1Option 1
Option 2Option 2
99% Confidence Allele Set =99% Confidence Allele Set = { { 10, 1110, 11 } } Database SearchingDatabase Searching
DNA Mixture ModelDNA Mixture ModelLinear Mixture AnalysisLinear Mixture Analysis
M.W. Perlin and B. Szabady, M.W. Perlin and B. Szabady, ““Linear mixture analysis: Linear mixture analysis: a mathematical approach to resolving mixed DNA samples,a mathematical approach to resolving mixed DNA samples,””
Journal of Forensic SciencesJournal of Forensic Sciences, November, 2001., November, 2001.
d = G x w d = G x w + e+ e
The Contributor ProblemThe Contributor Problem
DATADATAsample profilessample profiles
GENOTYPESGENOTYPESof of
contributorscontributors
WEIGHTSWEIGHTSof of
contributorscontributorsin samplesin samples
contributorscontributors
One SampleOne Sample
Sample C:Sample C:Unknown (A) 70%Unknown (A) 70%Unknown (G) 30%Unknown (G) 30%
1 ng DNA1 ng DNAPowerPlex16PowerPlex16
ABI/310ABI/310
samplesample
con
trib
uto
rsco
ntr
ibu
tors
Two SamplesTwo Samples
Sample A: Reference Sample A: Reference &&
Sample C:Sample C:Reference (A) 70%Reference (A) 70%Unknown (G) 30%Unknown (G) 30%
1 ng DNA1 ng DNAPowerPlex16PowerPlex16
ABI/310ABI/310
samplessamples
con
trib
uto
rsco
ntr
ibu
tors
Three SamplesThree Samples
Sample D:Sample D:(A) 50%(A) 50%(G) 50%(G) 50%
1, 1/2, 1/4, 1/8 ng DNA1, 1/2, 1/4, 1/8 ng DNAPowerPlex16PowerPlex16
ABI/310ABI/310
Sample C:Sample C:(A) 70%(A) 70%(G) 30%(G) 30%
Sample E:Sample E:(A) 30%(A) 30%(G) 70%(G) 70%
Two Contributors, No ReferenceTwo Contributors, No Reference
samplessamples
con
trib
uto
rsco
ntr
ibu
tors
samplessamples
con
trib
uto
rsco
ntr
ibu
tors
1 ng1 ng
1/8 ng1/8 ng
Collect Crime Scene EvidenceCollect Crime Scene Evidence
Generate DNA DataGenerate DNA Data
Review DNA DataReview DNA Data
Present Results to Legal SystemPresent Results to Legal System
The analyst will simply submit the items for DNA analysis, using the final data interpretation step to determine relevance to the ongoing investigation ... The bottleneck becomes the interpretation of analytical results and the technical review process. ... Although these processes are currently dependent upon manual applications, software solutions are emerging that can be integrated into an automated approach.