[1] Univ London London Sch Hyg & Trop Med, Dept Publ Hlth & Policy, Ctr Res Drugs & Hlth Behav, London WC1E 7HT, England
[2] Kings Coll London, Inst Psychiat, Natl Addict Ctr, London WC2R 2LS, England
[3] Cardiff Univ, Dept Gen Practice, Commun Skills Unit, Cardiff, S Glam, Wales