1. Second Military Medical University; Department of Health Statistics; No. 800 Xiangyin Road Shanghai Shanghai China 200433
2. Eastern Hepatobiliary Surgery Hospital; Department of Liver Transplantation; 225 CHANG HAI Road Shanghai Shanghai China 200438
3. Second Military Medical University; Department of Epidemiology; No. 800 Xiangyin Road Shanghai Shanghai China 200433
4. School of Public Health and Community Medicine, University of Washington; Department of Biostatistics; H655E, HSB Box #357232 Seattle WA USA 98198