1. Key Laboratory of Preclinical Study for New Drugs of Gansu Province, Basic Medical College, Lanzhou University, Lanzhou, Gansu, P.R. China
2. Institute of Epidemiology and Statistics, School of Public Health, Lanzhou University, Lanzhou, Gansu, P.R. China
3. Department of Epidemiology, School of Public Health, Brown University, RI, USA
4. Basic Medical College, Lanzhou University, Lanzhou, Gansu, 730000, P.R. China