1. Gastroenterology Section; Corporal Michael J. Crescenz VA Medical Center; Philadelphia PA USA
2. Center for Health Equity Research and Promotion; Corporal Michael J. Crescenz VA Medical Center; Philadelphia PA USA
3. Division of Gastroenterology; Department of Medicine; Hospital of the University of Pennsylvania; Philadelphia PA USA
4. Center for Clinical Epidemiology and Biostatistics; Perelman School of Medicine at the University of Pennsylvania; Philadelphia PA USA