1 Division of Gastroenterology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA.
2 Department of Medicine, Corporal Michael J. Crescenz VA Medical Center, Philadelphia, PA.
3 Division of Digestive Diseases, Yale University School of Medicine, New Haven, CT.
4 VA Connecticut Healthcare System, West Haven, CT.
5 Center for Clinical Epidemiology and Biostatistics, Department of Biostatistics and Epidemiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA.