1. University of New South Wales; National Drug and Alcohol Research Centre; National Drug and Alcohol Research Centre University of New South Wales Sydney New South Wales Australia 2052
2. London School of Hygiene and Tropical Medicine; Centre for Research on Drugs and Health Behaviour; Keppel Street London UK WC1E 7HT
3. ASL RM/E; Department of Epidemiology; Via di Santa Costanza, 53 Rome Italy 00199