Affiliation: | 1 Department of Biostatistics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, U.S.A. gyin{at}odin.mdacc.tmc.edu, 2 Department of Biostatistics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7420, U.S.A. cai{at}bios.unc.edu |