“No preset rules in DNA Forensics”: examples of errors and doubts in DNA casework that juries must tackle.

This does not read like CSI Miami. Wait, that one got cancelled. Thank you Jesus.

“A 2013 survey by the National Institute of Standards and Technology asked analysts from 108 labs to look at a three-person mixture and determine if a suspect’s DNA was present. Seventy percent of the analysts said the suspect might be in the mix; 24 percent said the data was inconclusive. Just six percent arrived at the truth: The suspect was not in the sample.

Not only do analysts vary in their interpretation of evidence, they also disagree over how certain to feel about the results. In another NIST survey, labs interpreting a two-person mixture came back with match probabilities that varied by 10 orders of magnitude. “Imagine if you take a pregnancy test and you send it to two different labs,” said Greg Hampikian, who authored the study on bias in the Atlanta rapist case, “and one said the odds are a billion to one that you’re pregnant, and the other said it’s 50-50.” The Marshall Project.

A study on contextual bias among lab analysts.

Similar cases with arguments about partial DNA profiles and disagreement in their results. 

Uncovering unscientific assumptions used in DNA
mixture analysis. These assumptions are committee-based. The following group and its NCFS equivalent has raised the ire of the IP’s Barry Scheck recently.

“The Scientific Working Group on DNA Analysis Methods (known as SWGDAM) acknowledged in their publication (Interpretation Guidelines for Autosomal STR Typing by Forensic DNA Testing Laboratories, 2010) that “[d]ue to the multiplicity of forensic sample types and the potential complexity of DNA typing results, it is impractical and infeasible to cover every aspect of DNA interpretation by a preset rule,” thereby keeping the door open for subjective interpretation by the DNA analyst. This door is also open for knowledgeable experts to challenge interpretation of that data, particularly when it comes to the most difficult DNA samples to interpret, Low Copy Number (LCN) mixtures.”


About csidds

Dr. Michael Bowers is a long time forensic consultant in the US and international court systems.
This entry was posted in Crime, criminal justice, CSI, death penalty, DNA mixtures, DNA profiling, Forensic Science, police crime labs, wrongful convictions and tagged , , , , , , , , . Bookmark the permalink.

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