1. Center for Clinical Epidemiology and Biostatistics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania;
2. Division of Rheumatology, Nemours/Alfred I. duPont Hospital for Children, Wilmington, Delaware;
3. Division of Gastroenterology, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania;
4. Clinical Epidemiology, HealthCore, Wilmington, Delaware; and
5. Rutgers Biomedical and Health Sciences, New Brunswick, New Jersey