From the Division of General Internal Medicine, Department of Medicine, University of Pennsylvania,* Leonard Davis Institute of Health Economics, University of Pennsylvania,† Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine,‡ Department of Biostatistics and Epidemiology,@ Division of Gastroenterology, Department of Medicine, University of Pennsylvania,∥, Veteran's Affairs Medical Center, Philadelphia, PA¶, Department of Surgery, University of Pennsylvania#, and The Wharton School, University of Pennsylvania**
This work was supported by a grant from the Agency for Health Care Policy and Research (HS06481).
Correspondence and reprint request to: Judy A. Shea, PhD, Division of General Internal Medicine, University of Pennsylvania, Ralston House 318, 3615 Chestnut Street, Philadelphia, PA 19104-2676.
Accepted for publication December 11, 1997.