1. Department of Biostatistics, School of Public Health, Cheeloo College of Medicine Shandong University Jinan Shandong P. R. China
2. Institute for Medical Dataology, Cheeloo College of Medicine Shandong University Jinan Shandong P. R. China
3. Department of Biostatistics, School of Public Health Peking University Beijing P. R. China
4. Shool of Mathematical sciences Peking University Beijing P. R. China