[1] Natl Univ Hlth Syst, Natl Univ Hosp, Univ Med Cluster, Div Resp & Crit Care Med, Singapore, Singapore
[2] Natl Univ Singapore, Yong Loo Lin Sch Med, Biostat Unit, Singapore, Singapore
[3] Natl Univ Hlth Syst, Alexandra Hosp, Fast & Chron Programmes, Singapore, Singapore
[4] Natl Univ Hlth Syst, Ng Teng Fong Gen Hosp, Dept Resp Med, Singapore, Singapore