1. Department of Internal Medicine, Seoul National University College of Medicine, Seoul 110-799, Korea.
2. Healthcare Research Institute, Seoul National University Hospital Healthcare System Gangnam Center, Seoul 135-984, Korea.
3. Department of Internal Medicine, Inje University Pusan Paik Hospital, Busan 614-735, Korea.
4. Department of Internal Medicine, Pusan National University School of Medicine, Busan 626-870, Korea.
5. Department of Internal Medicine, Kyungpook National University Medical School, Daegu 700-842, Korea.
6. Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam 463-707, Korea.