1. Liaoning Public Health and Anti‐epidemic Station, Shenyang, People's Republic of China
2. Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD
3. Public Health and Anti‐epidemic Station, Anshan Iron‐Steel Complex, Anshan, People's Republic of China
4. Labor Hygiene Research Institute of Anshan Iron‐Steel Complex, Anshan, People's Republic of China