[1] UNIV PENN, LEONARD DAVIS INST HLTH ECON, 3641 LOCUST WALK, PHILADELPHIA, PA 19104 USA
[2] DENVER GEN HOSP, EMERGENCY MED SERV, DENVER, CO 80204 USA
[3] UNIV COLORADO, HLTH SCI CTR, EMERGENCY MED RES CTR, DENVER, CO 80262 USA
[4] JOHNS HOPKINS UNIV, SCH HYG & PUBL HLTH, DEPT ENVIRONM HLTH SCI, DIV OCCUPAT HLTH, BALTIMORE, MD 21218 USA
[5] YALE UNIV, SCH MED, DEPT MED, RHEUMATOL SECT, NEW HAVEN, CT 06510 USA
[6] UNIV PENN, SCH MED, DIV GEN INTERNAL MED, PHILADELPHIA, PA 19104 USA
[7] UNIV PENN, SCH MED, DEPT MED, CLIN EPIDEMIOL UNIT, PHILADELPHIA, PA 19104 USA
[8] UNIV PENN, WHARTON SCH, DEPT HLTH CARE SYST, PHILADELPHIA, PA 19104 USA