[1] NHLBI, Div Lung Dis, NIH, Bethesda, MD 20892 USA
[2] Case Western Reserve Univ, Sch Med, Metrohlth Med Ctr, Cleveland, OH USA
[3] Harvard Univ, Sch Med, Dept Populat Med, Boston, MA USA
[4] Harvard Pilgrim Hlth Care Inst, Boston, MA USA
[5] Childrens Hosp, Div Gen Pediat, Boston, MA 02115 USA
[6] VA Puget Sound Hlth Care Syst, Hlth Serv Res & Dev, Seattle, WA USA
[7] Univ Washington, Div Pulm & Crit Care Med, Seattle, WA 98195 USA
[8] Dept Vet Affairs, Seattle, WA USA
[9] Univ Chicago, Dept Med, Asthma & COPD Ctr, Chicago, IL 60637 USA
[10] Univ Chicago, Dept Hlth Studies, Chicago, IL 60637 USA
[11] Univ Colorado, Sch Med, Dept Med, Denver, CO USA
[12] Tufts Univ, Tufts Med Ctr, Inst Clin Res & Hlth Policy Studies, Clin & Translat Sci Inst, Boston, MA 02111 USA