1. Corporal Michael J Crescenz VA Medical Center, Department of Gastroenterology, Philadelphia, Pennsylvania, USA
2. University of Pennsylvania, Perelman School of Medicine, Department of Medicine, Philadelphia, Pennsylvania, USA
3. University of Pennsylvania, Perelman School of Medicine, Department of Gastroenterology, Philadelphia, Pennsylvania, USA
4. Department of Epidemiology and Biostatistics, Center of Clinical Epidemiology and Biostatistics, University of Pennsylvania, Perelman School of Medicine, Philadelphia, Pennsylvania, USA
5. Department of Epidemiology and Biostatistics, University of Pennsylvania, Perelman School of Medicine, Philadelphia, Pennsylvania, USA