[1] Univ Penn, Perelman Sch Med, Div Pulm Allergy & Crit Care, Philadelphia, PA 19104 USA
[2] Kaiser Permanente Div Res, Oakland, CA USA
[3] Univ Penn, Palliat & Adv Illness Res PAIR Ctr, Perelman Sch Med, Philadelphia, PA 19104 USA
[4] Univ Penn, Wharton Sch, Dept Stat, Philadelphia, PA 19104 USA
[5] Univ Penn, Ctr Emergency Care Policy & Res, Dept Emergency Med, Perelman Sch Med, Philadelphia, PA 19104 USA