1 Department of Public Health, Environments, and Society, Faculty of Public Health and Policy, London School of Hygiene and Tropical Medicine, London WC1H 9SH, UK. Electronic address: adam.holland@bristol.ac.uk.
2 Department of Public Health, Environments, and Society, Faculty of Public Health and Policy, London School of Hygiene and Tropical Medicine, London WC1H 9SH, UK.
3 Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK.
4 Department of Epidemiology and Public Health, University College London, London, UK.
5 Drug and Alcohol Research Network, School of Psychology, Queens University Belfast, Belfast, UK.
6 National Institute for Health Research Evaluation Trials and Studies Coordinating Centre, Southampton, UK.