There was an
article in San Francisco magazine about the accuracy of DNA identification and the legal battles surrounding it. The article outlines the approach, wherein from a DNA sample, various locations are matched with the suspect's DNA. With 13 matches, the probability is about one in a trillion of it being anyone but the subject or an identical twin. But, due to degradation and other factors, fewer matches are used, and there the dispute seems to begin.
According to the FBI’s own population frequency tables—the ones crime labs generally use to calculate DNA rarity—the chance of finding a coincidental nine-locus match in the general population is about one in 754 million for whites, and one in 561 million for blacks, depending on certain genetic variables.
But it turns out that surveys of databases are showing 9-loci matches at a lot higher frequency. A DNA analyst in Arizona published some results at a conference, and a follow-up showed 90 9-loci matches in a database of 60,000 people.
Arizona, it turns out, wasn’t a fluke: Searches soon revealed similarly disquieting numbers in other state databases. In 2006, for example, a Chicago judge ordered a search of the Illinois database, which turned up 903 pairs that matched at nine loci or above, out of 220,000 people. A search of Maryland’s 30,000-person database reportedly found 32 pairs at nine or more loci. Clearly, something was going on.
As Marc Taylor, a former criminalist for the Los Angeles medical examiner, who now runs an independent crime lab in Ventura, puts it, “The bottom line is, we need to have some statisticians go in and find out what the hell is going on.”
What says our resident expert?
1 comment:
I have the rebuttals to this crap from lawyers who don't know what they're doing in an article at work, I'll post them later this week. But basically the claims are all from lawyers who don't know anything about this stuff. Bottom line? The science and statistics are sound.
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