1. Taishan Medical University, Taian, Shandong, P.R. China.
2. School of Medical and Health Sciences, Edith Cowan University, Perth, Australia.
3. Beijing Key Laboratory of Clinical Epidemiology, School of Public Health, Capital Medical University, Beijing, P.R. China.
4. Taishan Vocational College of Nursing, Taian, Shandong, P.R. China.