The gap between graduation rates of white and black students at the University of Michigan is the second highest among 11 similar elite universities, according to a study released Wednesday by an advocacy group for minority and low-income students. Although U-M's graduation rate of 67 percent for black students is higher than the national average of 40 percent, the fact that it is considerably lower than several peer institutions is cause for concern, said Kevin Carey, director of policy research at the Education Trust, a Washington-based think tank that conducted the study.