Supplementary Material for: The association between education and cognitive performance varies at different levels of cognitive performance: a quantile regression approach

Introduction Educational differences in cognitive performance among older adults are well-documented. Studies that explore this association typically estimate a single average effect of education on cognitive performance. We argue that the processes that contribute to the association between education and cognitive performance are unlikely to have equal effects at all levels of cognitive performance. In this study, we employ an analytical approach that enables us to go beyond averages to examine the association between education and five measures of global and domain-specific cognitive performance across the outcome distributions. Methods This cross-sectional study included 1780 older adults aged 58–68 years from the Longitudinal Aging Study Amsterdam (LASA). Conditional quantile regression was used to examine variation across the outcome distribution. Cognitive outcomes included Mini-Mental State Examination score (MMSE), crystallized intelligence, information processing speed, episodic memory, and a composite score of global cognitive performance. Results The results showed that the associations between education and different cognitive measures varied across the outcome distributions. Specifically, we found that education had a stronger association with crystallized intelligence, MMSE, and a composite cognitive performance measure in the lower tail of the performance distributions. The associations between education and information processing speed and episodic memory were uniform across the outcome distributions. Conclusion Larger associations between education and some domains of cognitive performance in the lower tail of the performance distributions implies that inequalities are primarily generated among individuals with lower performance, rather than among average and high performers. Additionally, the varying associations across some of the outcome distributions indicate that estimating a single average effect through standard regression methods may overlook variations in cognitive performance between educational groups. Future studies should consider heterogeneity across the outcome distribution.