[1] NIA, Lab Epidemiol Demog & Biometry, Bethesda, MD 20892 USA
[2] Tuscany Reg Hlth Agcy, Florence, Italy
[3] Azienda Sanitaria Firenze, Dept Geriatr Rehabil, Florence, Italy
[4] NIA, Longitudinal Studies Section, Clin Res Branch, Baltimore, MD 21224 USA