1. Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE 68198, USA
2. McGoogan Health Sciences Library, University of Nebraska Medical Center, Omaha, NE 68198, USA
3. Department of Internal Medicine, Southern Illinois University, Springfield, IL 62702, USA
4. Research and Development Service, John D. Dingell VA Medical Center, Detroit, MI 48201, USA
5. Research Service, VA Nebraska-Western Iowa Health Care System, Omaha, NE 68105, USA