1. Biostatistics Research Branch, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
2. Beijing International Center for Mathematical Research, Peking University, 100871, China.
3. School of Mathematical Sciences, Peking University, 100871, China.
4. Office for Epidemiology, Chinese Center for Disease Control and Prevention, 102206, China.
5. Department of Biostatistics, School of Public Health, Peking University, 100871, China.
6. Center for Statistical Science, Peking University, 100871, China.