1 Centre for Academic Primary Care, School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Clifton BS8 2PS, Bristol, UK
2 Nuffield Department of Primary Care Health Sciences, New Radcliffe House, Radcliffe Observatory Quarter, Woodstock Road, Oxford OX2 6GG, UK
3 Division of Primary Care, University of Nottingham, Floor 13, Tower Building, University Park, Nottingham NG7 2RD, UK
4 University of Southampton, Aldermoor Health Centre, Aldermoor Close, Southampton SO15 5ST, UK