[1] Univ Ulsan, Asan Med Ctr, Coll Med, Dept Internal Med,Div Pulmonol & Crit Care Med, Seoul, South Korea
[2] Univ Ulsan, Asan Med Ctr, Coll Med, Dept Clin Epidemiol & Biostat, Seoul, South Korea
[3] Univ Ulsan, Coll Med, Asan Med Ctr, Dept Internal Med,Div Pulmonol & Crit Care Med, 88 Olymp Ro 43 Gil, Seoul 05505, South Korea