[1] Med Univ S Carolina, Hollings Canc Ctr, Dept Psychiat & Behav Sci, Charleston, SC 29425 USA
[2] Med Univ S Carolina, Div Biostat & Epidemiol, Dept Med, Charleston, SC 29425 USA
[3] UCL, Dept Epidemiol & Publ Hlth, Canc Res UK Hlth Behav Res Ctr, London, England
[4] NHS Ctr Smoking Cessat & Training, London, England