1. Department of Health Statistics, College of Preventive Medicine, Third Military Medical University, Chongqing 400038, China
2. Department of Rehabilitation and Physiotherapy, Xinqiao Hospital, Third Military Medical University, Chongqing 400038, China
3. Soft College, Chongqing University of Posts and Telecommunications, Chongqing 400065, China
4. Department of Biological Sciences and Department of Asian Language and Literature, University of Washington, School of Arts and Sciences, Snohomish, WA 98290, USA