[1] Bangor Univ, Sch Healthcare Sci, Bangor, Gwynedd, Wales
[2] Univ Warwick, Sch Hlth & Social Studies, RCN Res Inst, Coventry CV4 7AL, W Midlands, England
[3] Cochrane Collaborat, Oxford, England
[4] London S Bank Univ, Fac Hlth & Social Care, London, England
[5] Royal Coll Physicians, NCGC, London NW1 4LE, England
[6] Royal Coll Anaesthetists, London, England