1. Department of Internal Medicine, SoonChunHyang University School of Medicine, Bucheon, Korea
2. Department of Medicine, Chung-Ang University Gwangmyeong Hospital, Gwangmyeong, Korea
3. Department of Statistics, SoonChunHyang University School of Medicine, Bucheon, Korea
4. Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea