1. College of Medical Information Engineering, Shandong First Medical University and Shandong Academy of Medical Sciences, Taian 271000, Shandong Province, P. R. China
2. College of Computer and Information Science and College of Software, Southwest University, Chongqing 400715, P. R. China
3. School of Public Health, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan 250118, Shandong Province, P. R. China