1. Division of Pulmonary and Critical Care Medicine, Department of MedicineSamsung Medical Center, Sungkyunkwan University School of Medicine Seoul Republic of Korea
2. Center for Clinical EpidemiologySamsung Medical Center Seoul Republic of Korea
3. Department of Clinical Research Design and Evaluation, SAIHSTSungkyunkwan University Seoul Republic of Korea
4. Division of Pulmonary Medicine and Allergy, Department of Internal MedicineHanyang University College of Medicine Seoul Republic of Korea
5. Division of Pulmonary, Allergy and Critical Care Medicine, Department of Internal MedicineSeoul St Mary's Hospital, College of Medicine, The Catholic University of Korea Seoul Republic of Korea
6. Department of EpidemiologyJohns Hopkins University Bloomberg School of Public Health Baltimore MD USA
7. Department of Internal MedicineKonkuk University School of Medicine Seoul Republic of Korea