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, an assistant professor of business and public policy 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.
Wolfers-Price examined 13 years during which time black players logged 83% of the minutes while 68% of referees were white. Did that really affect anything? The lead researcher, Justin Wolfers, tells Schwarz that an examination of the numbers suggests that "if you spray-painted one of your starters white, you'd win a few more games."
The Times interviewed various NBA players and coaches -- not one said on the record that they were aware of such a trend. And no one in the Times article suggests any such bias is conscious or intentional.