1. Institution of Epidemiology and Statistics, School of Public Health, Lanzhou University , 199 Donggang West Road, Lanzhou, Gansu 730000 , China
2. School of Public Health and Emergency Management, Southern University of Science and Technology, 1088 xueyuan Street, Shenzhen, Guangdong 518055, China
3. Workers’ Hospital of Jinchuan Corporation, Jinchuan Group CO., LTD, 53 Beijing Road, Jinchang, Gansu 737100, China