Birth cohort differences in fluid cognition in old age: comparisons of trends in levels and change trajectories over 30 years in three population-based samples.

Later-born cohorts of older adults tend to outperform earlier born on fluid cognition (i.e., Flynn effect) when measured at the same chronological ages. We investigated cohort differences in level of performance and rate of change across three population-based samples born in 1901, 1906, and 1930, drawn from the Gerontological and Geriatric Population Studies in Gothenburg, Sweden (H70), and measured on tests of logical reasoning and spatial ability at ages 70, 75, and 79 years. Estimates from multiple-group latent growth curve models (LGCM) revealed, in line with previous studies, substantial differences in level of performance where later-born cohorts outperformed earlier born cohorts. Somewhat surprisingly, later-born cohorts showed, on average, a steeper decline than the earlier-born cohort. Gender and education only partially accounted for observed cohort trends. Men outperformed women in the 1906 and 1930 cohorts but no difference was found in the 1901 cohort. More years of education was associated with improved performance in all three cohorts. Our findings confirm the presence of birth cohort effects also in old age but indicate a faster rate of decline in later-born samples. Potential explanations for these findings are discussed.