Now the race card is being played to attack NBA ref's May 2, 2007 Study of N.B.A. Sees Racial Bias in Calling Fouls By ALAN SCHWARZ An academic study of the National Basketball Association, whose playoffs continue tonight, suggests that a racial bias found in other parts of American society has existed on the basketball court as well. 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 last year, and was moved to do 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 N.B.A. denied a request for its underlying data, even with names of officials and players removed, because it feared that the leagues confidentiality agreement with referees could be violated if the identities were determined through box scores.