Cohort differences in cognitive aging and terminal decline in the Seattle Longitudinal Study.

Abstract

Life span researchers have long been interested in how and why fundamental aspects of human ontogeny differ between cohorts of people who have lived through different historical epochs. When examined at the same age, later born cohorts are often cognitively and physically fitter than earlier born cohorts. Less is known, however, about cohort differences in the rate of cognitive aging and if, at the very end of life, pervasive mortality-related processes overshadow and minimize cohort differences. We used data on 5 primary mental abilities from the Seattle Longitudinal Study (Schaie, 2005) to compare both age-related and mortality-related changes between earlier born cohorts (1886–1913) and later born cohorts (1914–1948). Our models covary for several individual and cohort differences in central indicators of life expectancy, education, health, and gender. Age-related growth models corroborate and extend earlier findings by documenting level differences at age 70 of up to 0.50 SD and less steep rates of cognitive aging on all abilities between 50 and 80 years of age favoring the later born cohort. In contrast, mortality-related models provide limited support for positive cohort differences. The later born cohort showed steeper mortality-related declines. We discuss possible reasons why often reported positive secular trends in age-related processes may not generalize to the vulnerable segment of the population that is close to death and suggest routes for further inquiry.

Secular Changes in Late-Life Cognition and Well-Being: Towards a Long Bright Future With a Short Brisk Ending?

“…To reconcile our findings with reports that secular advantages for later cohorts do not carry into late life (Gerstorf et al, 2011;Hülür et al, 2013), we heuristically sketch three scenarios for how cohort differences manifest in old age (Fries, 1980;Olshansky, Hayflick, & Carnes, 2002;Vaupel, 2010). The scenarios conjointly assume that (a) later-born cohorts live longer than earlier-born cohorts, (b) death late in life is preceded by a period of steep deterioration, and (c) average functioning at the time of death has not changed historically (i.e., people die at older ages, but are neither healthier nor sicker at death than before).…”

“…Secular increases favoring later-born cohorts in performance of adolescents and young adults on fluid intelligence measures have been widely documented (Flynn, 1999;Trahan, Stuebing, Fletcher, & Hiscock, 2014). Empirical studies have repeatedly shown that positive secular trends persist into late adulthood (Bowles, Grimm, & McArdle, 2005;Christensen et al, 2013;Finkel, Reynolds, McArdle, & Pedersen, 2007;Langa et al, 2008;Rönnlund & Nilsson, 2008;Schaie, Willis, & Pennak, 2005), but not up to the final years of old age (Gerstorf, Ram, Hoppmann, Willis, & Schaie, 2011;Hülür, Infurna, Ram, & Gerstorf, 2013). Adding to this body of research, with the current study, we have provided a comprehensive quantification of the nature and size of such trends in old age using data from participants residing in a narrowly defined geographical area.…”

Biomarkers of healthy ageing: expectations and validation

“…These associations are strongest in the age group up to about 75 years but tended to disappear in older populations (34,38) . Similar decreases of predictive power at higher age have been noted for other potential biomarkers (39,40) , although often there are not sufficient data on multiple age cohorts, especially the oldest old, available. Cohort and/or period effects may be partially responsible if there is a trend reversal or loss of predictive power at old age.…”

How Education Drives Demography and Knowledge Informs Projections

“…Although measures of age-specific functioning based on disability may be biased by for instance social and cultural influences -which could potentially bias comparisons across cohorts and nations, also research based on objective measures of performance, including assessments of cognitive functioning based on standardized tests, show that there are in fact improvements across subsequent cohorts among those aged 50 and above (Skirbekk et al 2013;Gerstorf et al 2011). Such gains are likely to have taken place earlier in some countries than in others, partly as educational expansions have taken place at different periods which thereby could contribute to differences in in age-specific cognitive functioning across countries.…”