1. Department of Epidemiology and Health Statistics, School of Public Health, Guangxi Medical University, Nanning, Guangxi, P.R. China
2. Department of Sanitary Chemistry, School of Public Health, Guangxi Medical University, Nanning, Guangxi, P.R. China
3. Department of Epidemiology and Biostatistics, College for Public Health & Social Justice, Saint Louis University, Saint Louis, MO, USA
4. School of Social Work, College for Public Health & Social Justice, Saint Louis University, St. Louis, MO, USA
5. Department of Environmental and Occupational Health, School of Public Health, Sun Yat-sen University, Guangzhou, Guangdong, PR China
6. Department of Maternal, Child and Adolescent Health, School of Public Health, Guangxi Medical University, Nanning, Guangxi, PR China