1. Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 06351, Republic of Korea
2. Center for Clinical Epidemiology, Samsung Medical Center, Seoul 06351, Republic of Korea
3. Department of Clinical Research Design & Evaluation, SAIHST, Sungkyunkawan University, Seoul 06351, Republic of Korea
4. Division of Pulmonary, Allery, and Critical Care Medicine, Department of Internal Medicine, Korea University Guro Hospital, Seoul 08308, Republic of Korea