You don’t know what you don’t know But does it matter? Or is everything inconclusive?

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  • You dont know what you dont know But does it matter? Or is everything inconclusive?

  • DisclaimerThe opinions or assertions contained herein are the private views of the author and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of DefenseIn fact, they may not even be the same views as those of my Technical Leader or my Boss, and they are both up on stage with me

  • Disclaimer (continued)To be honest, some things I may say today arent even my real opinionsIve been known to play Devils Advocate just to make things interesting(In other words, sometimes I stir the pot just for the fun of it)

  • What is this profile? (ID amp)

  • This profile isNot interpretableSingle source femaleSingle source male2 person mixture3 person mixtureCannot determine # of contributorsA no-brainer

  • What about this one? (Y amp)

  • This profile isNot interpretableSingle source 2 person mixture3 person mixtureCannot determine # of contributorsA no-brainerIt would be OK, but 11 at Y-GATA

  • Its the same sample!The first one is an Identifiler amp of Victims underwear.The second one is a Yfiler amp of the exact same extract.1 uL taken for ID amp (then diluted), followed by ~3 uL taken for Y amp from the same extract tube.(Other samples in the case show an Identifiler match from V evidence to S reference)

  • Yfiler profile of panties

  • Suspect Yfiler profile

  • Victim Identifiler profile

  • Suspect Identifiler profile

  • Alleles in common for V and SD2130111211*14812*23D7CSFD13*D19TPOXD5*FGA

  • Now what?What does this mean?Does this change your assessment of the ID profile from V underwear?You know there is a male in the sampleThat male shares some alleles with the femaleDid the enzyme sort through the shared alleles and only amplify DNA that came from female cells?

  • What do you think about original ID profile?Cannot interpretSingle source femaleMixture CONSISTENT with 2Mixture AT LEAST 2

  • Whats the point?You never know what you dont knowIn other words, you can never be 100% certain of anythingIs this bad?Uh oh, is all data inconclusive?Should we do CPI stat on every sample?# of contributors irrelevantEasy to explain but that whole stochastic drop out problem

  • Heres the pointYou must draw a line in the sand everytime you make an interpretationValidation studiesInterpretation guidelinesYour experienceIf it walks like a duck, talks like a duck, swims like a duck. Might as well call it a duck.

  • What do I say?I still interpret that profile as a single source female.I have to go with what I see.My validation studiesInterpretation guidelines/protocols My experiencePlus, my tech reviewer agrees or report doesnt go out.

  • Take a stand on the standIf its consistent with a two person mixture, go ahead and interpret it as such.If it appears to be a three person mixture, treat it that way.State your opinion, and be confident.Validation studies and mixture guidelines/protocols.Your experience. Your technical review process.

  • Should we do this?Section 3.6.5 SWGDAM

    Define how you determine # of contributors in your protocolsState it in your report

    3.6.5. Because assumptions regarding the origin of evidence or the number of contributors to a mixture can impact comparisons, the laboratory should establish guidelines for documenting any assumptions that are made when formulating conclusions.

  • WordingWe used to routinely sayA mixture of DNA profiles from at least two individuals was obtained from the...

    Now as much as possible we sayA mixture of DNA profiles consistent with originating from two individuals was obtained from the

  • But what ifHow do you handle it if challenged in court about the number of contributors?Heres what I do: (Not telling you to do this)Explain why I say 2 people (or 3)Explain the difference between consistent with 2 people and a mixture of 2 peopleIf I keep getting challenged.

  • Why do I bring this up?The interpretations that youll see during this workshop rely on being able to determine the number of contributorsThe CPI stat is pretty much the only thing to use when you dont know how many contributorsThe CPI stat has some limitations that affect how you can interpret a sample

  • These nifty clickersThere are no right or wrong answersAnswer as best you can the way your lab would do thingsWe can all learn how our lab compares to other labsNo one will know how you answered

  • Did you look at the examples we emailed or watched the videos?What email?I looked at them butI applied my labs interpretation to themI was going to do it on the plane, but there was this movie.