1. Center for Biostatistics; The Ohio State University Wexner Medical Center; Columbus OH 43221 USA
2. Novartis Pharmaceuticals Corporation; East Hanover NJ 07936 USA
3. Department of Statistics and Actuarial Science; The University of Hong Kong; Hong Kong
4. Department of Biostatistics; The University of Texas M.D. Anderson Cancer Center; Houston TX 77030 USA