[1] Massachusetts Gen Hosp, Tobacco Res & Treatment Ctr, Dept Med, Boston, MA 02114 USA
[2] Harvard Univ, Sch Med, Boston, MA 02114 USA
[3] Univ Lausanne, Dept Ambulatory Care & Community Med, Lausanne, Switzerland
[4] Univ Bristol, Dept Expt Psychol, Bristol, Avon, England
[5] Univ Oxford, Dept Primary Care Hlth Sci, Oxford, England