1. School of Public Health, Cheeloo College of Medicine, Shandong University, Ji'nan, Shandong, China.
2. Department of Geriatrics, Qilu Hospital, Cheeloo College of Medicine, Shandong Univeristy, Ji'nan, Shandong, China.
3. NHC Key Laboratory of Health Economics and Policy Research, Cheeloo College of Medicine, Shandong University, Ji'nan, Shandong, China.