1. Department of General Surgery, Affiliated Hospital of Qingdao University, Qingdao, China
2. Department of Hepatobiliary Surgery, Affiliated Hospital of Qingdao University, Qingdao, China
3. Department of General Surgery, Yantai Yuhuangding Hospital, Yantai, China
4. Department of Histology and Embryology, Binzhou Medical University, Yantai, China
5. Department of Epidemiology and Health Statistics, Qingdao University Medical College, Qingdao, China