From Queen's University, Kingston, Ontario, Canada; Institute for Clinical Evaluative Sciences and University of Toronto, Toronto, Ontario, Canada; Harvard Medical School and Harvard School of Public Health, Boston, Massachusetts; University of British Columbia, Vancouver, British Columbia, Canada; and Meyers Primary Care Institute of the University of Massachusetts Medical School, Fallon Clinic Foundation, and Fallon Community Health Plan, Worcester, Massachusetts. (At 2007-06-05)