Department of Statistics, Columbian College of Arts and Sciences, The George Washington University, Washington, DC, USA.|Department of Biostatistics, Mailman School of Public Health, Columbia University, New York, NY, USA.|Department of Epidemiology and Biostatistics, Memorial Sloan-Kettering Cancer Center, New York, NY, USA.|Department of Biostatistics, Mailman School of Public Health, Columbia University, New York, NY, USA.