Societal gender equality and spousal cognitive interdependence: A random-intercept cross-lagged analysis across 20 countries.

BACKGROUND: Spouses often show concordant cognitive trajectories, but whether this reflects a within-dyad prospective association or merely shared environments and assortative mating remains unresolved, and whether it varies across cultural contexts is unknown. METHODS: We harmonised longitudinal data from 69,703 couples aged 50 years and older, contributing 91,115 couple-wave transitions across 20 countries, from four ageing cohorts (CHARLS, HRS, SHARE and MHAS); a fifth cohort, KLoSA, had cognitive data in a single wave and contributed to the cross-sectional analyses only. Random-Intercept Cross-Lagged Panel Models separated within-dyad prospective associations from stable between-dyad confounding; country-specific partner effects were pooled and examined by meta-regression against the UN Gender Inequality Index (GII) and Hofstede's Individualism Index. RESULTS: Traditional cross-lagged models overestimated partner effects by 65-68%. After removing stable between-dyad variance, bidirectional within-dyad prospective associations persisted (β = 0.033 in both directions, P < 0.001). In an exploratory ecological meta-regression, the husband-to-wife association was inversely related to national gender inequality (GII b = - 0.222, Knapp-Hartung P = 0.022), being larger in more egalitarian countries. This association was significant in 18 of 20 leave-one-country-out iterations but was attenuated to non-significance after adjustment for GDP per capita (b = - 0.205, Knapp-Hartung P = 0.153). CONCLUSIONS: Spousal cognitive concordance is not fully explained by stable between-dyad confounding such as assortative mating, although the within-dyad associations that remain are small. Their magnitude varied across countries in a pattern associated at the ecological level with societal gender equality, an exploratory finding that requires replication.