[1] Penn State Univ, Coll Med, Dept Hlth Evaluat Sci, Hershey, PA 17033 USA
[2] Brigham & Womens Hosp, Div Resp, Boston, MA 02115 USA
[3] Thomas Jefferson Med Coll, Philadelphia, PA USA
[4] Univ Wisconsin, Madison, WI USA
[5] Univ Calif San Francisco, Div Pulm & Crit Care Med, San Francisco, CA 94143 USA
[6] Natl Jewish Med & Res Ctr, Denver, CO USA