Joint modeling of cognitive aging and survival: Evaluation of birth cohort differences

We examined generational differences in the associations between cognitive functioning (i.e., level and rate of change) and survival after age 70. Data were drawn from two population-based cohorts born in 1901–1907 (n = 1106) and 1930 (n = 896), each systematically sampled from the same city population and assessed on the same cognitive battery at ages 70, 75, 79, 85, 88, 90, 92, 95, 97, 99, and 100. Cognitive performance was indexed using a composite score derived from tests of spatial ability, perceptual-motor speed, and reasoning. Mortality data, obtained from the Swedish national population register, were complete for >99 % of the 1901–07 cohort and 39 % of the 1930 cohort (last update: April 2023). We fitted joint models for longitudinal cognitive change and survival, controlling for sex and education. Across both cohorts, a one SD lower cognitive level was associated with a 1.43-fold higher mortality hazard, 95 % HDI [1.34, 1.53]. Models including cohort interactions revealed stronger effects of cognitive level in the 1901–07 cohort (HR = 1.50 [1.39, 1.61]) compared to the 1930 cohort (HR = 1.26 [1.14, 1.40]). Moreover, steeper rates of cognitive decline were associated with increased mortality risk in the 1930 cohort (HR = 1.74 [1.40, 2.17]), but not in the 1901–07 cohort (HR = 1.07 [0.97, 1.77]). These findings suggest that cognitive level is a stronger mortality predictor among earlier-born cohorts, whereas rate of cognitive decline plays a larger role in later-born cohorts, highlighting cohort-specific differences in how cognitive aging informs survival probability.