1. Center for Health Quality, Outcomes, and Economoic Research, Veterans Affairs Medical Center, Bedford, Mass and Department of Health Services, Bos-ton University School of Public Health, Boston, Mass,
2. Center for Health Quality, Outcomes, and Economoic Research, Veterans Affairs Medical Center, Bedford, Mass and Department of Health Services, Bos-ton University School of Public Health, Boston, Mass
3. Center for Health Quality, Outcomes, and Economoic Research, Veterans Affairs Medical Center, Bedford, Mass and Department of Mathematics and Statistics, Boston University, Boston, Mass
4. The Health Institute, New England Medical Center, Boston, Mass
5. Veterans Health Ad-ministration, VISN 16, Jackson, Miss