1 Institute for Applied Health Research, Glasgow Caledonian University, Glasgow G4 0BA, United Kingdom. Electronic address: Laura.Williamson@gcu.ac.uk.
2 Drug and Alcohol Research Centre, University of Middlesex, United Kingdom.
3 Imperial College London, and London School of Hygiene and Tropical Medicine, United Kingdom.
4 Austrian Public Health Institute (GOEG), Stubenring 6, 1010 Vienna, Austria; Sigmund Freud Private University (SFU), Freud Platz 1, 1020 Vienna, Austria.