1. Institute of Epidemiology and Statistics, School of Public Health, Lanzhou University, Lanzhou, Gansu, China
2. College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, Gansu, China
3. Institute of Social Medicine and Health Management, School of Public Health, Lanzhou University, Lanzhou, Gansu, China
4. Xiangya School of Public Health, Central South University, Changsha, Hunan, China