Affiliation: | 1. School of Statistics and Mathematics, Zhongnan University of Economics and Law, Wuhan, Hubei, China;2. School of Mathematics and Statistics, Wuhan University, Wuhan, Hubei, China;3. Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, NC, U.S.A.;4. Department of Pediatrics, University of North Carolina at Chapel Hill, Chapel Hill, NC, U.S.A. |