1. Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center; Sungkyunkwan University School of Medicine; Seoul Korea
2. Department of Health Sciences and Technology, SAIHST; Sungkyunkwan University; Seoul Korea
3. Department of Clinical Research Design and Evaluation, SAIHST; Sungkyunkwan University; Seoul Korea
4. Center for Clinical Epidemiology; Samsung Medical Center; Seoul Korea
5. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine; Ilsan Paik Hospital, Inje University College of Medicine; Goyang South Korea
6. Department of Epidemiology and Welch Center for Prevention, Epidemiology, and Clinical Research; Johns Hopkins University Bloomberg School of Public Health; Baltimore Maryland USA