1. Division of Clinical and Translational Sciences, Department of Internal Medicine, Medical School; The University of Texas Health Science Center at Houston; Houston, TX 77030 U.S.A.
2. Biostatistics/Epidemiology/Research Design Core, Center for Clinical and Translational Sciences; The University of Texas Health Science Center at Houston; Houston, TX 77030 U.S.A.
3. Department of Biostatistics; The University of Texas MD Anderson Cancer Center; Houston, TX 77030 U.S.A.