1. Department of Pediatric Surgery, Korea University Ansan Hospital, Korea University College of Medicine, Seoul, Korea.
2. Department of Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
3. Department of Pediatric Surgery, Kyung Hee University Hospital, Kyung Hee University College of Medicine, Seoul, Korea.
4. Department of Pediatric Surgery, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea.
5. Department of Preventive Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea.