Effect of family income on cognition in older adults in China: an instrumental-variables decomposition analysis

Abstract

BackgroundCognitive skills are important for making decisions, including those that involve health and financial outcomes. For older populations in developing countries such as China, individuals frequently have to make important decisions without the aid of professionals specialising on those topics, and levels of cognitive ability are often not high. We investigated the effect of family income on older adult cognition, and income-related inequalities and their determinants in adult cognition. MethodsWe used nationally representative data from second wave of the China Health and Retirement Longitudinal Study, which was conducted in 2013 and involved 17 663 respondents aged 45 years and older. Two measures based on word recall and mathematical calculation were used as proxies for different dimensions of adult cognition—episodic memory and intact mental status—and we related these cognitive measures to adult health and socioeconomic outcomes. Using the variation of total investment in fixed assets and tax income across provinces as instrumental variables, we aimed to identify the potential causal effects of family income on cognition. The concentration index was used to estimate income-related inequalities in adult cognition. Pooling the method of instrumental variables and the decomposition of concentration index, we further decomposed the inequality into its determinants. Findings1% growth in family income was estimated to drive a 3·2% increase (0·13 units [95% CI 0·09–0·16], p<0·001) increase in episodic memory and a 2·7% increase (0·20 units [0·14–0·24], p<0·001) in intact mental status. The concentration index was 0·053 for episodic memory and 0·054 for intact mental status. The decomposition analysis indicated that most of the inequalities in cognition could be explained by family income, age, alcohol consumption, tobacco smoking status, and participation in mahjong. The linear regression method consistently underestimated the contribution of family income to inequalities in adult cognition. InterpretationA financial gain might generate more detectable improvement in cognition in older adults. Our findings justify broad policy interventions that promote public health through increasing the availability of economic resources. This study highlights potential determinants of adult cognition problems in developing contexts, providing a reference for policy makers in China and other developing countries seeking to improve the health of disadvantaged groups. FundingChina Scholarship Council (grant numbers 201706280307 and 201806280021), US PEPPER Center Scholar Award (grant number P30AG021342), National Institute on Aging (US National Institutes of Health; grant numbers R03AG048920 and K01AG053408).