1. Department of Epidemiology, Shanxi Medical University School of Public Health, Taiyuan 030001, China
2. Office for Cancer Prevention and Research, Affiliated Cancer Hospital of Zhengzhou University/Henan Cancer Hospital, Zhengzhou 450008, China
3. Department of Obstetrics, the First Affiliated Hospital, Shanxi Medical University, Taiyuan 030001, China
4. Department of Chronic Disease Epidemiology, Yale School of Public Health, New Haven, 06520 CT, USA
5. Department of Surgery, Yale University School of Medicine, New Haven 06520, USA
6. Department of Environmental Health Sciences, Yale School of Public Health, New Haven, 06520 CT, USA