1. Cadre Health Department, Qingdao Municipal Hospital, Qingdao, Shandong 266011, P.R. China
2. Cadre Health Department, East Hospital of Qingdao Municipal Hospital, Qingdao, Shandong 266071, P.R. China
3. Cadre Health Department, West Hospital of Qingdao Municipal Hospital, Qingdao, Shandong 266005, P.R. China