1. Department of Public Health Science, Graduate School of Public Health, Seoul National University, Seoul, Korea.
2. Department of Orthopaedic Surgery, Chung-Ang University College of Medicine, Seoul, Korea.
3. Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, Seongnam, Korea.
4. Department of Obstetrics and Gynecology, The Catholic University of Korea, College of Medicine, Seoul, Korea.