[1] NIA, Longitudinal Studies Sect, Clin Res Branch, NIH, Baltimore, MD 21224 USA
[2] NIA, Lab Epidemiol Demog & Biometry, NIH, Baltimore, MD 21224 USA
[3] Italian Natl Inst Res & Care Aging, Lab Clin Epidemiol, Florence, Italy
[4] Univ Perugia, Inst Gerontol & Geriatr, I-06100 Perugia, Italy