1. Department of Surgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
2. Department of Surgery, Soonchunhyang University Seoul Hospital, Seoul, Korea.
3. Department of Biostatistics, Soonchunhyang University College of Medical Sciences, Seoul, Korea.
4. Department of Surgery, Chonbuk National University Hospital, Jeonju, Korea.
5. Institute of Health Insurance & Clinical Research, National Health Insurance Service Ilsan Hospital, Goyang, Korea.
6. Department of Surgery, National Health Insurance Service Ilsan Hospital, Goyang, Korea.