Prof. David Kaye says on his blog that yesterday’s L.A. Times article on DNA, cold hits, and statistics is not balanced, and portrays one side of a debate as though it is the only valid viewpoint:
[A]n article in the May 3 Los Angeles Times claims to have uncovered a national scandal of sorts. The reporters describe a recent “cold hit” case that they say
is emblematic of a national problem, The Times has found. [¶] Prosecutors and crime labs across the country routinely use numbers that exaggerate the significance of DNA matches in “cold hit” cases, in which a suspect is identified through a database search. [¶] Jurors are often told that the odds of a coincidental match are hundreds of thousands of times more remote than they actually are, according to a review of scientific literature and interviews with leading authorities in the field.
The article maintains that
[I]n cold hit cases, the investigation starts with a DNA match found by searching thousands, or even millions, of genetic profiles in an offender database. Each individual comparison increases the chance of a match to an innocent person. [¶] Nevertheless, police labs and prosecutors almost always calculate the odds as if the suspect had been selected randomly from the general population in a single try. [¶] The problem will only grow as the nation’s criminal DNA databases expand. They already contain 6 million profiles.
This description portrays one approach to the issue as if it is the consensus in the scientific literature. It is not. There is disagreement about the need to adjust a random-match probability. Furthermore, if one counts the number of peer-reviewed articles on the subject, the dominant view is that adjustment is not necessary.
So according to Prof. Kaye, the dominant view according to peer-reviewed articles on the subject is portrayed as the minority view (indeed, I note that the view is hardly discussed, as if nobody takes it seriously).
Prof. Kaye’s post has more excellent insights on the right way to view this controversy. Go here to read it.