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  • Cybergenetics :: Reliable Interpretation of Stochastic DNA Evidence
    STR genetic loci At each cycle of the random PCR branching process a DNA fragment is re amplified or not with some probability Low amounts of DNA template or additional PCR cycles increase this inherent amplification peak variability DNA analysts follow interpretation guidelines that use peak height thresholds These laboratory calibrated thresholds attempt to tame uncertainty by declaring that peaks over threshold are true alleles whereas those under threshold are not This all or none threshold process can discard considerable identification information since a DNA peaks below threshold often represent actual amplified genetic material and b quantitative STR peak heights can tell us how much of each individual contributed to the sample Moreover while threshold methods may reduce the possibility of interpretation error they cannot eliminate it entirely The 2010 SWGDAM DNA interpretation guidelines have the effect of raising STR review thresholds in an attempt to reduce uncertainty by discarding more DNA data Unfortunately this approach can make highly informative DNA evidence less useful by either artificially lowering a match score or rendering it entirely inconclusive However the same guidelines offer two mechanisms for scientifically preserving DNA match information The new SWGDAM guidelines permit the use of a validated probabilistic genotype method that can be used in place of peak thresholds paragraph 3 2 2 Modern statistics enables computers to capture data uncertainty in probability models The peak height uncertainty can then be used to help infer genotype possibilities and their associated probabilities By concentrating genotype probability more heavily on those allele pairs that are better supported by the data DNA match information to the actual culprit can be preserved The new guidelines also allow combining DNA data paragraph 3 4 3 1 Such combination is a well established method in statistical science implemented using a joint likelihood function that

    Original URL path: http://www.cybgen.com/information/presentations/2010/CSFS/Perlin_Reliable_interpretation_of_stochastic_DNA_evidence/page.shtml (2016-02-12)
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  • Cybergenetics :: Overcoming DNA Stochastic Effects
    At each cycle of the random PCR branching process a DNA fragment is re amplified or not with some probability Low amounts of DNA template or additional PCR cycles increase this inherent amplification peak variability DNA analysts follow interpretation guidelines that use peak height thresholds These laboratory calibrated thresholds attempt to tame uncertainty by declaring that peaks over threshold are true alleles whereas those under threshold are not This all or none threshold process can discard considerable identification information since a DNA peaks below threshold often represent actual amplified genetic material and b quantitative STR peak heights can tell us how much of each individual contributed to the sample Moreover while threshold methods may reduce the possibility of interpretation error they cannot eliminate it entirely The 2010 SWGDAM DNA interpretation guidelines have the effect of raising STR review thresholds in an attempt to reduce uncertainty by discarding more DNA data Unfortunately this approach can make highly informative DNA evidence less useful by either artificially lowering a match score or rendering it entirely inconclusive However the same guidelines offer two mechanisms for scientifically preserving DNA match information The new SWGDAM guidelines permit the use of a validated probabilistic genotype method that can be used in place of peak thresholds paragraph 3 2 2 Modern statistics enables computers to capture data uncertainty in probability models The peak height uncertainty can then be used to help infer genotype possibilities and their associated probabilities By concentrating genotype probability more heavily on those allele pairs that are better supported by the data DNA match information to the actual culprit can be preserved The new guidelines also allow combining DNA data paragraph 3 4 3 1 Such combination is a well established method in statistical science implemented using a joint likelihood function that coherently explains the

    Original URL path: http://www.cybgen.com/information/presentations/2010/NEAFS/Perlin_Overcoming_DNA_stochastic_effects/page.shtml (2016-02-12)
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  • Cybergenetics :: Explaining the likelihood ratio in DNA mixture interpretation
    is a standard information measure for stating the support for a simple hypothesis i e a single assertion relative to its logical alternative After Alan Turing s LR methods cracked the German Enigma code during World War II LR usage became widespread The LR is ubiquitous in the physical biological social economic computer and forensic sciences First introduced into biological identification through paternity testing the LR enjoys unparalleled international usage as the most informative DNA mixture statistic Yet American crime labs shun the LR and prefer to report DNA inclusion statistics that they find easier to explain in court Such inclusion methods variously termed PI CPI CPE or RMNE use less of the DNA data typically discarding a million fold factor of identification information Thus highly informative DNA mixture evidence can be reported as inconclusive or assigned an unrealistically low match score Unfortunately minimizing DNA evidence leads to a failure to identify criminals with an adverse effect on public safety To make the LR more acceptable to American analysts and their juries we need more intuitive ways to explain the LR Fortunately the LR can be expressed by Bayes theorem in several equivalent ways Stated in plain English these alternative

    Original URL path: http://www.cybgen.com/information/presentations/2010/ISHI/Perlin_Explaining_the_likelihood_ratio_in_DNA_mixture_interpretation/page.shtml (2016-02-12)
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  • Cybergenetics :: More Informative DNA Identification: Computer Reinterpretation of Existing Data
    2010 talk Download Handout Download PowerPoint Abstract Forensic analysts work hard producing DNA data from complex biological evidence They then expend further effort interpreting their data However current DNA interpretation guidelines can limit the amount of information that they are permitted to report As more challenging data e g mixed low level degraded enters the laboratory workflow we see scientists working ever harder to extract diminishing identification information Computer interpretation using probabilistic genotypes is now allowed under the SWGDAM guidelines Section 3 2 2 The computer can use validated quantitative models instead of qualitative thresholds to interpret and match the DNA evidence Therefore a computer assistant enables an analyst to extract all the information present in their data A previous study with the New York State Police DNA lab compared quantitative computer and qualitative human interpretation We assessed the relative identification information derived from the same DNA evidence mixture items which ranged from simple mixtures to low copy and three contributor challenges TrueAllele 174 computer interpretation preserved on average a million times more identification information as measured by DNA match statistics Importantly the study also showed on a large data set that quantitative computation could interpret evidence that qualitative review

    Original URL path: http://www.cybgen.com/information/presentations/2010/MAFS/David_More_informative_DNA_identification_computer_reinterpretation_of_existing_data/page.shtml (2016-02-12)
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  • Cybergenetics :: Forensic DNA Analysis: An Introduction
    teaching a Continuing Legal Education CLE course on Forensic DNA Analysis An Introduction at Duquesne University in The Cyril H Wecht Institute of Forensic Science and Law The course will introduce computer interpretation of DNA evidence and its courtroom admissibility The case example is the recent Blairsville dentist homicide where a computer extracted more DNA identification information than the FBI s review On the night of April 12 2006 dentist John Yelenic was brutally murdered in his Blairsville PA home A year later Pennsylvania State Trooper Kevin Foley boyfriend of Dr Yelenic s estranged wife was charged with the crime Under the victim s fingernails was a mixture of DNA containing mainly the victim plus a trace amount 6 7 of an unknown contributor The FBI s interpretation of the DNA evidence gave a 13 000 chance of match with Foley relative to a random person Considering that almost 13 million people reside in Pennsylvania this was not an overwhelming statistic However some mixture interpretation methods can make better use of the DNA data for a more informative result Prosecutor Krastek asked Dr Perlin to re examine this DNA mixture using Cybergenetics TrueAllele 174 computer approach The computer mathematically processed the fingernail DNA data and found a match statistic of 189 billion The prosecution also asked Dr Robin Cotton the former Cellmark lab director to conduct an independent human review of the DNA evidence Her method yielded a match statistic of 23 million On February 18 2009 there was a pretrial hearing in Indiana County on the admissibility of the two outside expert DNA evidence interpretations SDAG Krastek presented the relevant law and case precedents Drs Perlin and Cotton each explained the scientific foundations of their respective methods to the court and were cross examined at length Judge William Martin

    Original URL path: http://www.cybgen.com/information/presentations/2010/DUCLE/Perlin_Krastek_Collins_Forensic_DNA_analysis_An_introduction/page.shtml (2016-02-12)
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  • Cybergenetics :: Preserving DNA Information
    Annual Meeting Cleveland OH 2 Oct 2010 Talk PowerPoint presentation with live audio recording of the National Association of Medical Examiners 2010 talk Download Transcript Download Handout Download PowerPoint Abstract Medical examiners carefully preserve biological specimens in order to achieve the best scientific results And they expect DNA laboratories to extract maximal identification information from those specimens Indeed DNA lab work is exemplary But there is wide variation in the

    Original URL path: http://www.cybgen.com/information/presentations/2010/NAME/Perlin_Preserving_DNA_information/page.shtml (2016-02-12)
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  • Cybergenetics :: Profiles in Productivity: Greater Yield at Lower Cost with Computer DNA Interpretation
    Forensic Science Society Sydney Australia 9 Sep 2010 Talk PowerPoint presentation with live audio recording of the Australian and New Zealand Forensic Science Society 2010 talk Download Transcript Download Handout Download PowerPoint Abstract DNA evidence can pose interpretation challenges when it is mixed damaged degraded or in low amounts The resulting human interpretation bottleneck introduces backlogs With an inconclusive result reprocessing additional DNA items to produce a reportable match score entails further reagent cost laboratory time and human effort We examined 88 DNA mixture items from reported cases We classified these items into three groups simple N 35 intermediate 20 and complex 33 As item complexity increased the fraction that yielded a reportable match score decreased from 49 simple to 25 intermediate and 21 complex For example complex items would need five DNA assays and reviews in order to produce one reportable match score Cybergenetics TrueAllele 174 Casework uses a probability modeling approach with statistical computer search TrueAllele objectively infers genotypes from DNA data and subsequently matches them with other genotypes e g suspect or database The model includes common data artifacts such as PCR stutter relative amplification degraded DNA mixture weight peak uncertainty and stochastic effects Uncertainty in variables

    Original URL path: http://www.cybgen.com/information/presentations/2010/ANZFSS/Perlin_Profiles_in_productivity_Greater_yield_at_lower_cost_with_computer_DNA_interpretation/page.shtml (2016-02-12)
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  • Cybergenetics :: Scientific Combination of DNA Evidence: A Handgun Mixture in Eight Parts
    M W Perlin and M Greenhalgh Scientific combination of DNA evidence A handgun mixture in eight parts Twentieth International Symposium on the Forensic Sciences of the Australian and New Zealand Forensic Science Society Sydney Australia 8 Sep 2010 Talk PowerPoint presentation with live audio recording of the Australian and New Zealand Forensic Science Society 2010 talk Download Transcript Download Handout Download PowerPoint Abstract In a recent criminal case a handgun was swabbed for touch DNA in four separate locations Low template DNA was recovered from each swab and individually STR amplified in duplicate A two person DNA mixture was seen in each of the resulting eight PCR products Computer interpretation of the DNA mixtures with TrueAllele 174 probabilistic modeling yielded a definite no uncertainty 80 85 major contributor genotype at two of the four STR profiles This definite genotype matched the suspect with a likelihood ratio LR of over a quadrillion to one However the minor contributor genotypes were not resolved in any of the four DNA templates having respective mixture weights of 15 20 35 and 40 Probabilistic modeling though permits construction of a joint likelihood function that treats each PCR experiment independently Statistically combining the eight STR data

    Original URL path: http://www.cybgen.com/information/presentations/2010/ANZFSS/Perlin_Scientific_combination_of_DNA_evidence_A_handgun_mixture_in_eight_parts/page.shtml (2016-02-12)
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