[1] Univ Nottingham, Div Epidemiol & Publ Hlth, Nottingham NG5 1PB, England
[2] Univ Nottingham Hosp, Dept Resp Med, Nottingham NG5 1PB, England
[3] Univ Nottingham, Nottingham Resp Res Unit, Nottingham NG5 1PB, England
[4] Hlth & Social Care Informat Ctr, Clin Audit Support Unit, Leeds LS1 6AE, W Yorkshire, England
[5] Univ Nottingham Hosp, Dept Thorac Surg, Nottingham NG5 1PB, England