1 Institute of Health and Society, Newcastle University, Baddiley-Clark Building, Richardson Road, Newcastle Upon Tyne, NE2 4AX, UK. Electronic address: nick.steen@ncl.ac.uk.
2 Health Services Research Unit, Aberdeen University, 3rd Floor, Health Sciences Building, Foresterhill, Aberdeen, AB25 2ZD, UK.
3 Institute of Health and Society, Newcastle University, Baddiley-Clark Building, Richardson Road, Newcastle Upon Tyne, NE2 4AX, UK.
4 Clinical Epidemiology Program, Ottawa Hospital Research Institute and Department of Medicine, University of Ottawa, Centre for Practice-Changing Research (CPCR), 501 Smyth Road, Room 1286, Ottawa, Ontario K1H 8L6, Canada.
5 College of Medicine, Swansea University, Institute of Life Science 2, Singleton Park, Swansea, SA2 8PP, UK.