1. C. M. Clancy is director of the Center for Outcomes and Effectiveness Research and J. M. Eisenberg is administrator of the Agency for Health Care Policy and Research, U.S. Department of Health and Human Services (HHS), 2101 East Jefferson Street, Rockville, MD 20852, USA. The views expressed here are those of the authors and do not necessarily represent the position of the Agency for Health Care Policy and Research or of HHS.