[1] ST John God Hosp, Stillorgan, Co Dublin, Ireland
[2] Kings Coll London, MRC Soc Genet & Dev, Psychiat Res Ctr, Inst Psychiat, London, England
[3] Natl Addict Ctr, Inst Psychiat, Tobacco Res Unit, London, England
[4] Taylor Ctr, S Essex Partnership NHS Trust, Southend Sea SS4 1RB, Essex, England
[5] Inst Psychiat, Natl Addict Ctr, Tobacco Res Unit, London, England
[6] Kings Coll London, Psychiat Res Ctr, MRC Soc Genet & Dev, London, England