[1] Hosp Univ Penn, Pulm & Crit Care Med, 3400 Spruce St, Philadelphia, PA 19104 USA
[2] Univ Penn, Leonard Davis Inst Hlth Econ, Philadelphia, PA 19104 USA
[3] Denver Hlth & Hosp, Hosp Med, Denver, CO USA
[4] Univ Colorado, Sch Business, Denver, CO USA
[5] Univ Colorado, Internal Med, Anschutz Med Campus, Denver, CO USA