[1] Cardiff Univ, Sch Med, Cochrane Inst Primary Care & Publ Hlth, Cardiff CF10 3AX, S Glam, Wales
[2] Univ Bristol, Sch Social & Community Med, Natl Inst Hlth Res Sch Primary Care Res, Ctr Acad Primary Care, Bristol, Avon, England
[3] Cardiff Univ, Sch Med, South East Wales Trials Unit, Cardiff CF10 3AX, S Glam, Wales
[4] Univ Oxford, Nuffield Dept Primary Care Hlth Sci, Oxford, England
[5] Swansea Univ, Swansea Ctr Hlth Econ, Swansea, W Glam, Wales
[6] Univ Dundee, Sch Med, Populat Hlth Sci, Dundee, Scotland
[7] Univ Wales Hosp, Publ Hlth Wales Microbiol Cardiff, Specialist Antimicrobial Chemotherapy Unit, Cardiff CF4 4XW, S Glam, Wales
[8] Univ Nottingham, Ctr Evidence Based Dermatol, Nottingham NG7 2RD, England
[9] Pk House Surg, Surrey, England
[10] Univ Toronto, North York Gen Hosp, Dept Family & Community Med, Toronto, ON, Canada
[11] Univ Toronto, North York Gen Hosp, Dalla Lana Sch Publ Hlth, Toronto, ON, Canada