1 Nottingham Clinical Trials Unit, Applied Health Research Building, University of Nottingham, University Park, Nottingham, NG7 2RD, UK. eleanor.mitchell@nottingham.ac.uk.
2 Nottingham Clinical Trials Unit, Applied Health Research Building, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
3 NMAHP Research Unit, Glasgow Caledonian University, Glasgow, G4 0NA, UK.
4 Bristol Trials Centre, Population Health Sciences, Bristol Medical School, University of Bristol, 1-5 Whiteladies Road, Bristol, BS8 1NU, UK.
5 Clinical Research Department, London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT, UK.