(Note: “The Power of the Jump”™ is a semi-regular feature of this site, documenting examples of the Los Angeles Times’s use of its back pages to hide information that its editors don’t want you to see.)
Above the fold in their Sunday edition, the L.A. Times asks in its lead story: “How reliable is DNA in identifying suspects?” The deck headline: “A discovery leads to questions about whether the odds of people sharing genetic profiles are sometimes higher than portrayed. Calling the finding meaningless, the FBI has sought to block such inquiry.”
The story is by our old friends Jason Felch and Maura Dolan, who so badly botched the statistics in this area before.
Here’s their lede:
State crime lab analyst Kathryn Troyer was running tests on Arizona’s DNA database when she stumbled across two felons with remarkably similar genetic profiles.
The men matched at nine of the 13 locations on chromosomes, or loci, commonly used to distinguish people.
The FBI estimated the odds of unrelated people sharing those genetic markers to be as remote as 1 in 113 billion. But the mug shots of the two felons suggested that they were not related: One was black, the other white.
In the years after her 2001 discovery, Troyer found dozens of similar matches — each seeming to defy impossible odds.
Wow! So the matches Troyer found were statistically unexpected, right?
Mmmm . . . not so much. Here’s the crucial passage, which was buried at page A20:
Indeed, experts generally agree that most — but not all — of the Arizona matches were to be expected statistically because of the unusual way Troyer searched for them.
In a typical criminal case, investigators look for matches to a specific profile. But the Arizona search looked for any matches among all the thousands of profiles in the database, greatly increasing the odds of finding them.
Well, there you have it! And you have only to turn to Page A20 to learn this! And, of course, every loyal L.A. Times reader does exactly that!
Just ask around! You don’t know anyone who just scans the headlines and the front page, do you?
What’s that? That describes most people you know?
Well . . . . that’s OK, I guess. I’m sure none of those people will end up as jurors on our DNA cases . . .
UPDATE: David Kaye has an excellent post on this that helps put it all in context.