Anand Viswanathan, MD, PhD, Walter A. Rocca, MD, MPH and Christophe Tzourio, MD, PhD From the Department of Neurology and Clinical Trials Unit (A.V.), Massachusetts General Hospital and Harvard Medical School, Boston; Division of Epidemiology (W.A.R.), Department of Health Sciences Research and Department of Neurology, College of Medicine, Mayo Clinic, Rochester, MN; INSERM (C.T.), Unit 708 Neur