1. Division of Biostatistics; The University of Texas Health Science Center at Houston; 1200 Pressler St, Houston, TX 77030 U.S.A.
2. Department of Biostatistics; The University of Texas MD Anderson Cancer Center; Houston, TX 77030 U.S.A.
3. Department of Surgical Oncology; The University of Texas MD Anderson Cancer Center; Houston, TX 77030 U.S.A.