“Basically, it suggests that if you spray-painted one of your starters white, you’d win a few more games”

The blog Politics, Economics, and other Stuff notes a new Justin Wolfers paper on racial bias among referees in the NBA (Update: there is more at the end following up on a WSJ editorial on regulating wooden versus aluminum bats):

New Justin Wolfers Paper makes the NYT, by Stefan:  The NYT reports on the new Justin Wolfers paper: Racial Discrimination Among NBA Referees. This seems to be an ideal setting for difference-in-difference identification, so the results would of the face of it strike me as most likely credible.

A coming paper by a University of Pennsylvania professor and a Cornell University graduate student says that, during the 13 seasons from 1991 through 2004, white referees called fouls at a greater rate against black players than against white players.

Justin Wolfers ... at the Wharton School, and Joseph Price, a Cornell graduate student in economics, found a corresponding bias in which black officials called fouls more frequently against white players, though that tendency was not as strong.

They went on to claim that the different rates at which fouls are called “is large enough that the probability of a team winning is noticeably affected by the racial composition of the refereeing crew assigned to the game.”

N.B.A. Commissioner David Stern said in a telephone interview that the league saw a draft copy of the paper late last year, and was moved to conduct its own study this March using its own database of foul calls, which specifies which official called which foul. “We think our cut at the data is more powerful, more robust, and demonstrates that there is no bias,” Mr. Stern said.

Three independent experts asked by The Times to examine the Wolfers-Price paper and materials released by the N.B.A. said they considered the Wolfers-Price argument far more sound. ...

The paper by Mr. Wolfers and Mr. Price has yet to undergo formal peer review before publication... The three experts who examined the Wolfers-Price paper and the N.B.A.’s materials were Ian Ayres of Yale Law School, the author of “Pervasive Prejudice?” and an expert in testing for ... racial bias...; David Berri of California State University-Bakersfield, the author of “The Wages of Wins,” which analyzes sports issues using statistics; and Larry Katz of Harvard University, the senior editor of the Quarterly Journal of Economics. ...

To investigate whether such bias has existed in sports, Mr. Wolfers and Mr. Price examined data from publicly available box scores. They accounted for factors like the players’ positions, playing time and All-Star status; each group’s time on the court (black players played 83 percent of minutes, while 68 percent of officials were white); calls at home games and on the road; and other relevant data.

But they said they continued to find the same phenomenon: that players who were similar in all ways except skin color drew foul calls at a rate difference of up to 4 ½ percent depending on the racial composition of an N.B.A. game’s three-person referee crew. ...

Mr. Wolfers and Mr. Price also report a statistically significant correlation with decreases in points, rebounds and assists, and a rise in turnovers, when players performed before primarily opposite-race officials.

“Player-performance appears to deteriorate at every margin when officiated by a larger fraction of opposite-race referees,” they write. The paper later notes no change in free-throw percentage. “We emphasize this result because this is the one on-court behavior that we expect to be unaffected by referee behavior.”

Mr. Wolfers and Mr. Price claim that these changes are enough to affect game outcomes. Their results suggested that for each additional black starter a team had, relative to its opponent, a team’s chance of winning would decline from a theoretical 50 percent to 49 percent and so on...

“Basically, it suggests that if you spray-painted one of your starters white, you’d win a few more games,” Mr. Wolfers said.

Update: Andrew Leigh comments on the Wolfers and Price research.

Update: [removed - comments are focused on the basketball element and this update about baseball on a different topic was a distraction].