The knee of the Tiger

Update, July 2008: I suspect that this post does not describe Tiger's now-famous knee injury, but I want nonetheless to acknowledge that yes, I realize how dumb it sounds now. So noted.

During Tiger Woods's victorious final round at the PGA championship on Sunday, Woods stumbled awkwardly as he pumped his fist after holing a birdie putt on the eighth hole. I was watching the round with two friends, and none of us saw anything of concern in the stumble, but the CBS announcers immediately speculated that Tiger had incurred a knee injury. (Come to think of it, they may have said ankle first, but they soon settled on knee.) For many holes afterwards, they relentlessly attributed every bump in Tiger's road to victory to his allegedly hurt knee, in spite of no limps or grimaces to bear out the theory. When Woods clinched the victory with spectacularly huge swings, the knee narrative disappeared. I found this to be an unusually clear demonstration of selection bias, and one that illustrated more general problems with sports journalism: the announcers had more incentive to set up a dramatic narrative than to evaluate the evidence in front of them. With the narrative established, they supported it at every opportunity and then wordlessly abandoned it as it proved to be nonsense.