[1] Duke Univ, Dept Med, Div Pulm Allergy & Crit Care Med, Durham, NC 27710 USA
[2] Univ Penn, Perelman Sch Med, Palliat & Adv Illness Res Ctr, Philadelphia, PA 19104 USA
[3] Univ Penn, Perelman Sch Med, Dept Med, Div Pulm Allergy & Crit Care Med, Philadelphia, PA 19104 USA
[4] Univ Penn, Perelman Sch Med, Leonard Davis Inst Hlth Econ, Philadelphia, PA 19104 USA
[5] Univ Penn, Perelman Sch Med, Renal Electrolyte & Hypertens Div, Philadelphia, PA 19104 USA
[6] Univ Penn, Perelman Sch Med, Dept Biostat Epidemiol & Informat, Philadelphia, PA 19104 USA
[7] Univ Penn, Perelman Sch Med, Dept Med Eth & Hlth Policy, Philadelphia, PA 19104 USA
[8] Kaiser Permanente, Div Res, Oakland, CA USA
[9] Univ Chicago, Dept Med, Sect Pulm & Crit Care Med, 5841 S Maryland Ave, Chicago, IL 60637 USA