1. Department of Family Medicine; Sahmyook Medical Center; Seoul Korea
2. Department of Biostatistics; College of Medicine; The Catholic University of Korea; Seoul Korea
3. Department of Family Medicine; Korea University Ansan Hospital; College of Medicine; Korea University; Ansan-si Gyeonggi-do Korea
4. Department of Pediatrics; Korea University Ansan Hospital; College of Medicine; Korea University; Ansan-si Gyeonggi-do Korea