[1] Harvard Univ, Massachusetts Eye & Ear Infirm, Sch Med, Tobacco Res & Treatment Ctr, Boston, MA 02114 USA
[2] Harvard Univ, Massachusetts Gen Hosp, Sch Med, Pulm Crit Care Unit, Boston, MA 02114 USA
[3] Boston Univ, Sch Publ Hlth, Dept Social & Behav Sci, Boston, MA 02215 USA
[4] Harvard Univ, Massachusetts Gen Hosp, Sch Med, Ctr Child & Adolescent Hlth Policy, Boston, MA 02115 USA
[5] Univ Massachusetts, Survey Res Ctr, Boston, MA 02125 USA
[6] Harvard Univ, Sch Med, Div Gen Med, Massachusetts Gen Hosp, Boston, MA 02115 USA