Peer effects in golf

Tim Harford posts about a new piece of economics research finding no peer effects in professional golf tournaments. That is, according to the researchers, golfers aren't affected by the quality of their playing partners in tournaments.

I've long been skeptical of peer effects in golf. But the general finding doesn't (as far as I know) address the key specific question: does being paired with Tiger Woods on Sunday hurt other golfers? Just about everyone thinks so, but I'm skeptical because there's a simple explanation for the appearance of a Tiger Effect.

That explanation is this: intimidation aside, Tiger is the best golfer in the world. Therefore, if he and another player are contending to win a tournament, the other player's performance is by definition more of an aberration than Tiger's. (Any player who is tied or nearly tied with Tiger on Sunday has overachieved relative to Tiger.) Therefore, if Tiger and his playing partners do what we would normally expect of them, they would create the sense of Tiger intimidating the other players into Sunday collapses. Utterly ordinary expected performances would create the same Tiger Effect that golf analysts and fans now perceive.

Obviously, this reasoning does not disprove a real Tiger Effect. But any test of the effect should account for this explanation, the fact that courses generally get harder on Sunday, and other reasons why Tiger's playing partners may not be wilting but simply finding their level on Sundays.

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.