Sunday, May 21, 2006

Oh Man.

As if the internet did not provide enough distractions already, Tyler Cowen points me towards a bunch of sports economics blogs which discuss data-driven examinations of conventional wisdom in sports. For at least some of the posts, I clearly need to read the book "The Wages of Wins" because they have computed their own measures of player performance that I need to evaluate and understand before I will accept their conclusions. Overall, though, they make some interesting arguments.

In the vein of sports economics, let me briefly describe some of the findings in Will Hauser's term paper on NBA referees. Using data for the complete 2005-2006 NBA regular season, Will shows that home teams, on average, do, in fact, have fewer fouls called on them while at home. The raw difference in mean fouls per game between the home and visiting teams is -1.15 fouls. This difference is roughly the same when examined in a regression with controls for day of season, point margin throughout the game (as measured by the score difference at the end of each quarter), and team and opponent fixed effects (i.e., the coefficient is identified by comparing the games the same teams play against each other home versus away).

There are two main explanations for this finding. First, officials have an incentive to slant their calls toward the home team because of social rewards (cheers)/punishments (boos) from the crowd. Second, teams/players perform differently at home versus the road (e.g., road teams are tired from traveling, and this causes them to foul more). Unfortunately, we cannot distinguish between these two explanations for the result (but since this is a course on social effects, the officials story is preferred).

So how important is one foul per game? Very conservative, back of the envelope calculations suggest that 1 foul translates into slightly more than 1 point per game. During the regular season 5% of games were won by a single point (and 7% of games went into overtime). Thus, a single point is not irrelevant. Will points out that in 2004-2005 the Cleveland Cavaliers missed the playoffs by 1 game after losing 3 games on the road by 1 point (but only 1 game at home by 1). Thus the home foul advantage might have kept the Cavs out of the playoffs last season.

Further, it is possible that officials also favor the home team on traveling, 3 seconds, and close out-of-bounds calls. If true, this would further increase teams' home court advantages.

When we started this project, the initial expectation was that officials would be more prone to crowd influence when the crowd was very intense (e.g., late in close games). However, the opposite result was found. Quarter by quarter analysis indicates that the home-road differential is largest in the first quarter and declines each quarter and is not significant in the fourth quarter (and non-existent in OT). Also, there is no home-road differential in games televised nationally on ABC. These two findings suggest that officials "raise their game" during big moments. In economic terms, they are likely aware that the NBA will pay more attention to blown calls at key moments, and the costs of punishment from their bosses probably outweighs the effect of the crowd.

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