1. Department of Neurology, Massachusetts General Hospital, Boston, Massachusetts, U.S.A.;
2. Department of Neurology, Beth Israel Deaconess Medical Center, Boston, Massachusetts, U.S.A.;
3. Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts, U.S.A.;
4. Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts, U.S.A.; and
5. Department of Health Care Policy, Harvard Medical School, Boston, Massachusetts, U.S.A.