Education and Cognitive Aging: Accounting for Selection and Confounding in the Danish Registry-SHARE Data Linkage

Abstract

Earlier studies report inconsistent associations between education and cognitive aging. We assess the association accounting for selective dropout due to death or dementia, and, in a sub-sample, accounting for confounding by early life intelligence. Data from the Danish component of the Survey of Health, Ageing and Retirement in Europe (N = 3400) were linked to registry data (education records, dementia diagnoses and mortality), and The Danish Conscription Database (youth intelligence measures for 854 men). Word recall and verbal fluency were assessed up to 4 times over 10 years (2004-2013) and combined by averaging the Z-scores. We estimated a joint model linking a time-to-event model for dementia or death to a linear mixed-effects model for cognitive change. Rate of cognitive decline was slower among people with high education compared to low education (β = 0.112, 95% confidence interval (CI): 0.056, 0.170). Adjusting for youth intelligence did not attenuate the association between education and cognitive decline (β unadjusted = 0.136, 95% CI: 0.028, 0.244 vs β adjusted = 0.145, 95% CI: 0.022, 0.269). The results suggest that higher education may slow cognitive decline in later life. In this sample, results changed little when accounting for selective attrition and confounding by intelligence.