1. Department of Statistics, George Mason University, 4400 University Drive, Fairfax, Virginia 22030, U.S.A.
2. Department of Biostatistics, CB 7420, University of North Carolina, Chapel Hill, North Carolina 27599, U.S.A.
3. Amgen Inc., One Amgen Center Drive, Thousand Oaks, California 91320, U.S.A.