1. Section of Digestive Diseases and Nutrition, Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City
2. Section of Digestive Diseases and Nutrition, Department of Medicine, Veterans Affairs Medical Center, Oklahoma City, Oklahoma
3. Department of Biostatistics and Epidemiology, University of Oklahoma Health Science Center, Oklahoma City
4. Section of Gastroenterology, Department of Medicine, George E. Wahlen Veterans Affairs Medical Center, Salt Lake City, Utah