1. Department of Pediatrics, Bucheon St. Mary's Hospital, The Catholic University of Korea College of Medicine, Buchoen, Korea.
2. Department of Biostatistics, The Catholic University of Korea College of Medicine, Seoul, Korea.
3. Department of Pediatrics, Seoul St. Mary's Hospital, The Catholic University of Korea College of Medicine, Seoul, Korea.
4. Department of Pediatrics, St. Vincent Hospital, The Catholic University of Korea College of Medicine, Suwon, Korea.
5. Department of Pediatrics, Yeouido St. Mary's Hospital, The Catholic University of Korea College of Medicine, Seoul, Korea.