Erin Murphy co-authors report on efficacy of familial DNA searches

Erin MurphyProfessor Erin Murphy and a team of scientists have co-authored a report in the journal PLOS ONE on California’s method of searching existing DNA databases for potential family members of an unknown suspect who left DNA at a crime scene. California is the only state that has published their statistical methods for such familial DNA searches. The report, titled “The Influence of Relatives on the Efficiency and Error Rate of Familial Searching,” investigated the rate of false positives, as well as the rates of misidentification of distant relatives as first-degree relatives.

The study found that familial DNA searches do a good job of locating a relative if one is in the database, and conversely that a search is also unlikely to return a match that appeared to be related to the crime scene source, but in fact was not. However, the results also showed that a more distant relative in the existing DNA database could have up to a 42% chance of being incorrectly labeled as a first-degree relative of the person who left the crime scene DNA.

Murphy and co-authors Rori Rohlfs, Yun Song, and Montgomery Slatkin expressed concern in the report about the unintended consequences of these kinds of misleading results. “It has been well documented that familial searching is apt to disproportionately affect African American families, due to the greater representation of those groups in DNA databases and the high rate of intra-racial procreation,” they wrote. “It takes only one member of a large and varied family tree to render every father, brother, half-brother, cousin, half-cousin, uncle, nephew and so on vulnerable to scrutiny and surreptitious sampling by law enforcement officers.”

The report has garnered attention from the Los Angeles Times and on LiveScience.com. "We as a society have said that certain people, because of their behavior, have forfeited their genetic privacy," Murphy told the Los Angeles Times. "The thing that I find troubling is that we're saying that certain people who haven't done anything but are related to people who have also forfeit their genetic privacy."

Watch a video detailing the research methods for the report (3 min):

Posted on August 16, 2013

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