1 Population Health Research, MRC/CSO Social and Public Health Sciences Unit & Robertson Centre for Biostatistics, Institute of Health and Well Being, University of Glasgow, Berkeley Square, 99 Berkeley Street, Glasgow G3 7HR, UK.
2 Flat 1/1, 14 Willowbank Crescent, Glasgow, UK.
3 Royal Cornwall Hospital, University of Exeter Medical School, Truro, UK.
4 Primary Care Research Group, University of Exeter Medical School, St Luke's Campus, Exeter, UK.