Acknowledgements We thank Professor Luke Vale, Dr Diane Stockton and participants at the Faculty of Public Health conference, Aviemore, Scotland, November 2011 and UK Society for Behavioural Medicine conference, Stirling, Scotland, December 2011 for helpful comments. Funding This work was supported by the Medical Research Council National Preventive Research Initiative Phase 2 [G0701874]; see http://www.npri.org.uk. The Funding Partners relevant to this award are: British Heart Foundation; Cancer Research UK; Department of Health; Diabetes UK; Economic and Social Research Council; Medical Research Council; Research and Development Office for the Northern Ireland Health and Social Services; Chief Scientist Office; Scottish Government Health Directorates; The Stroke Association; Welsh Assembly Government and World Cancer Research Fund. The Health Economics Research Unit is funded by the Chief Scientist Office of the Scottish Government Health and Social Care DirectoratePeer reviewedPostprin