1. School of Public Health, North China University of Science and Technology, No. 21 Bohai Road, Caofeidian District, Tangshan 063200, Hebei, China
2. Qindao University Medical College Affiliated Yantai Yuhuangding Hospital, Yantai 264001, Shandong, China
3. Key Laboratory of Coal Mine Health and Safety of Hebei Province, School of Public Health, North China University of Science and Technology, Tangshan 063210, Hebei, China