There is substantial heterogeneity in cognitive aging trajectories. Although the number of individuals showing cognitive decline increases with age, significant proportions remain stable or show gains. The aim of this study was to investigate birth cohort differences regarding proportions of individuals showing cognitive decline, stability, or gain between ages 70 and 79. We analyzed longitudinal data from three Swedish birth cohorts from the Gothenburg H70 Birth Cohort Studies, born 1901-02, 1906-07 and 1930, measured on four cognitive measures (i.e., verbal meaning, figure identification, logical reasoning and spatial ability). We used the standard error of measurement (SEM=s√(1-r_xx) at baseline (i.e., 70 years of age) to categorize participants as showing cognitive decline (if scores decreased by >1 SEM between ages 70 and 79), cognitive stability (if change was ≤1SEM), or cognitive gain (if increasing by >1 SEM).

Analyses, using χ²- tests, showed that a substantial proportion remained stable over the 9-year period. Our findings also indicated significant cohort differences for all four cognitive measures, with weak to moderate effect sizes. Interestingly earlier born cohorts contained a higher proportion of participants showing cognitive gain and a smaller proportion showing cognitive decline, compared to later born cohorts. Possible explanations for these cohort differences may relate to cohort differences in cognitive reserve, selective survival and psychometric properties of the cognitive tests. These findings have implications for instance regarding the debate concerning postponing retirement age, and the use of cognitive tests in evaluations of for example work capability. © 2019 Karlsson P, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.