1. Department of Epidemiology and Health Statistics, School of Public Health and Management, Ningxia Medical University, Yinchuan, China
2. Public Administration Research Centre, Department of Public Health and Management, Ningxia Medical University, Yinchuan, China
3. Department of Hygienic Chemistry, School of Public Health and Management, Ningxia Medical University, Yinchuan, China
4. Department of Occupational and Environmental Health, School of Public Health and Management, Ningxia Medical University, Yinchuan, China