Michael Ussher1
, Paul Aveyard2
, Tim Coleman3
, Lianne Straus4
, Robert West5
, Bess Marcus6
, Beth Lewis7
and Isaac Manyonda8 
1Division of Community Health Sciences, St. George's University of London, London, SW17 0RE, UK
2Department of Primary Care and General Practice, University of Birmingham, Edgbaston, B15 2TT, UK
3School of Community Health Sciences, Division of Primary Care, Queen's University Medical Centre, Nottingham, NG7 2UH, UK
4Barcelona Centre for International Health Research (CRESIB), Hospital Clínic de Barcelona, Universitat de Barcelona, Rosselló 132, 4a planta, 08036 Barcelona, Spain
5Cancer Research UK Health Behaviour Research Centre, Department of Epidemiology and Public Health, University College London, 2-16 Torrington Place, London, WC1E 6BT, UK
6Department of Community Health and Department of Psychiatry and Human Behavior, Brown University, 121 South Main Street, Providence, Rhode Island, 02903, USA
7School of Kinesiology, University of Minnesota, 209 Cooke Hall, 1900 University Ave, Minneapolis, MN 55455, USA
8Department of Obstetrics and Gynecology, St George's Hospital, Blackshaw Road, London, SW17 0QT, UK