Aim: The aim of the present study was to investigate possible birth cohort differences in the proportion of individuals showing cognitive decline, stability or gain from age 70 to 79.

Method: We used data from three cohorts born in 1901-02, 1906-07, and 1930 measured at ages 70 and 79 years on four cognitive measures (i.e. spatial ability, figure identification, verbal meaning, and logical reasoning). We used the standard error of measurement (SEM=) 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).

Findings: χ²-tests indicated statistically significant birth cohort differences on all four cognitive measures, with weak to moderate effect sizes. For all four cognitive measures earlier born cohorts contained a smaller proportion of participants showing cognitive decline, and a larger proportion of participants showing gain, compared to later born cohorts. This was particularly evident when comparing the 1901-02 and 1930 cohorts.

Conclusion: These cohort differences may relate to cohort differences in cognitive reserve, selective survival, or psychometric properties of the cognitive tests.