1. Department of Health Statistics, School of Public Health, Shanxi Medical University, No. 56 Xinjian South Road, Yingze District, Taiyuan 030001, China
2. Department of Epidemiology and Biostatistics, Southeast University, 87 Ding Jiaqiao Road, Nanjing 210009, China
3. Department of Statistics, University of Auckland, 38 Princes Street, Auckland Central, Auckland 1010, New Zealand