[1] Univ York, Dept Hlth Sci, York Trials Unit, York YO10 5DD, N Yorkshire, England
[2] Univ York, Dept Hlth Sci, York Trials Unit, Surg Trials & Hlth Sci, York, N Yorkshire, England
[3] Univ Bristol Sch Med, Ctr Acad Primary Care, Populat Hlth Sci, Bristol, Avon, England
[4] Univ West England, Sch Hlth & Social Wellbeing, Emergency Care, Bristol, Avon, England