[1] Univ Birmingham, Primary Care Clin Sci, Birmingham, W Midlands, England
[2] Univ Birmingham, Primary Care Clin Sci, Birmingham, W Midlands, England
[3] Univ Birmingham, Dept Publ Hlth Epidemiol & Biostat, Birmingham, W Midlands, England
[4] Univ Manchester, Inst Populat Hlth, Ctr Primary Care, Manchester, Lancs, England
[5] Univ Oxford, Nuffield Dept Primary Care Hlth Sci, Oxford, England
[6] Univ Birmingham, Sch Hlth & Populat Sci, Birmingham, W Midlands, England
[7] Univ Hosp Leicester NHS Trust, Dept Cardiac & Pulm Rehabil, Leicester, Leics, England
[8] Primary Care Res Network Cent England, Telford, Shrops, England
[9] Royal Wolverhampton NHS Trust, New Cross Hosp, Wolverhampton WV10 0QP, W Midlands, England