1. From the Departments of Epidemiology and Medicine and the Welch Center for Prevention, Epidemiology, and Clinical Research, the Johns Hopkins Medical Institutions, Baltimore, MD (JB, LJA, and EG); the National Institute on Aging, National Institutes of Health, Baltimore, MD (ERM); and the Division of Biostatistics, National Center for Epidemiology, Instituto de Salud Carlos III, Madrid, Spain (RP