[1] Univ Glasgow, Western Infirm, Dept Resp Med, Glasgow G11 6NT, Lanark, Scotland
[2] Univ Glasgow, Dept Gen Practice, Glasgow G12 0RR, Lanark, Scotland
[3] Univ Glasgow, Robertson Ctr Biostat, Glasgow G12 8QQ, Lanark, Scotland
[4] Stobhill Gen Hosp, Dept Res & Dev, Glasgow G21 3UT, Lanark, Scotland