Studies of gender differences and individual variability in age-related phenomena are being carried out to: 1) determine the "normal" range of variability in human aging, 2) identify potential sources of variability which may be responsive to intervention, and 3) determine if there are subgroups of individuals who are more susceptible or resistant to various aspects of aging. The research combines the use of sophisticated statistical methodologies and the unique time depth and multidisciplinary breadth of the existing BLSA data base to examine issues related to the concepts of "normal" and "successful" aging, as well as to increase the power of traditional research designs. The statistical methods used include longitudinal regression models, time dependent proportional hazards analysis, and finite mixture models. Major findings include that on average systolic pressure is relatively stable in men and women until approximately age 45, increases at 5-8 mm Hg/decade in middle age, then accelerates in men and stabilizes in women. Diastolic pressure increases at 1 mm Hg/decade at all ages in men, whereas in women the rate of change in diastolic pressure increases in middle age and then plateaus and may decline after age 70. Additional findings include that BLSA cross-sectional and longitudinal findings are more similar than has been observed in studies of unscreened samples, that there is no evidence of gender cross-over in this group of healthy men and women, and that compared to previous studies of unscreened samples, healthy BLSA men and women show a weaker association between baseline blood pressure and subsequent rate of blood pressure change. Also, in a study of age- and gender-specific reference ranges for hearing level (see Project Z01 AG 00628-07 LSB), findings indicate that in screened samples of BLSA men and women, changes in hearing threshold relative to the baseline audiogram of an average of 10 dB or more at 2, 3 and 4 kHz in either ear increase with age and follow-up time in men, but little change occurs in women at all ages. These findings represent significant contributions to the theoretical and methodological development of biomedical risk factor studies, as well as to an increased understanding of the dynamics of the aging process. Research is underway to develop more refined methods of studying variability in aging in order to develop theoretically and methodologically sound approaches to risk factor analysis which account for changes in an individual's covariates over time and the possibility that individuals differ in susceptibility or resistance to aging processes.