David Leonhardt reports on Justin Wolfers' research with point spreads in today's New York Times. The title of the piece is "Sad Suspicions About Scores in Basketball" -- NCAA basketball, that is.
Mr. Wolfers has collected the results of nearly every college basketball game over the last 16 years. In a surprisingly large number of them, it turns out that heavy favorites just miss covering the spread. He considered a number of other explanations, but he thinks there is only one that can explain the pattern. Point shaving appears to be occurring in about 5 percent of all games with large spreads.
... Smaller favorites -- teams favored by 12 or fewer points -- beat the spread almost exactly 50 percent of the time, showing how good those oddsmakers are at their jobs. But heavy favorites cover in only 47 percent of their games. There is little chance that the difference is due to randomness.
This is not persuasive by itself, because there are some obvious explanations besides point shaving. Heavy favorites may remove their best players at the end of the game, for instance, or simply slack off, not caring what their winning margin is.
But here's Mr. Wolfers's smoking gun: this slacking off seems to happen only when a game is decided by something close to the point spread. Heavy favorites actually blow away the spread just as often as everyone else. But they win by barely more than the spread a lot less often than slight favorites do.
There is a strange dearth of games in which 12-point favorites win by, say, 13 or 16 points. And there are a lot of games that they win by 11 points or slightly less. There is just no good explanation for this.
Through correspondence, I know that Wolfers is also looking at NBA data, under the hypothesis that long term monetary incentives limit the practice in the pro game. That is ongoing work which is not in the paper or in Leonhardt's story.
Another view of this topic will be presented at a Symposium on Sports Law at Willamette College next week. Among other papers is "The Beauty of Bets: Wagers as Compensation for Professional Athletes," by Jeffrey Standen. Beauty is in the eye of the beholder, it seems. Hopefully that paper, along with others from the symposium, will be available soon as well.