1. From the Clinical Epidemiology Unit, General Medicine Division (D.E.S., Y.C., L.H.B.), Massachusetts General Hospital, Boston, Mass; the Department of Medicine (M.C.F., A.S.G.), University of California, San Francisco, Calif; the Division of Research (A.S.G., N.K.P., N.U.), Kaiser Permanente of Northern California, Oakland, Calif; and the Departments of Epidemiology and Biostatistics (A.S.G.), University of California, San Francisco, Calif.