Does education moderate gender disparities in later-life memory function? A cross-national comparison of harmonized cognitive assessment protocols in the United States and India

Causal Effects of Schooling on Memory at Older Ages in Six Low- and Middle-Income Countries: Nonparametric Evidence With Harmonized Datasets

OBJECTIVES

Higher schooling attainment is associated with better cognitive function at older ages, but it remains unclear whether the relationship is causal. We estimated causal effects of schooling on performances on the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) word-recall (memory) test at older ages in China, Ghana, India, Mexico, Russia, and South Africa.

METHODS

We used harmonized data (n = 30,896) on older adults (≥50 years) from the World Health Organization Study on Global Ageing and Adult Health. We applied an established nonparametric partial identification approach that bounds causal effects of increasing schooling attainment at different parts of the schooling distributions under relatively weak assumptions.

RESULTS

An additional year of schooling increased word-recall scores by between 0.01 and 0.13 SDs in China, 0.01 and 0.06 SDs in Ghana, 0.02 and 0.09 SDs in India, 0.02 and 0.12 SDs in Mexico, and 0 and 0.07 SDs in South Africa when increasing schooling from never attended to primary. No results were obtained for Russia at this margin due to the low proportion of older adults with primary schooling or lower. At higher parts of the schooling distributions (e.g., high school or university completion), the bounds cannot statistically reject null effects.

DISCUSSION

Our results indicate that increasing schooling from never attended to primary had long-lasting effects on memory decades later in life for older adults in 5 diverse low- and middle-income countries.

Characterizing Multimorbidity Prevalence and Adverse Outcomes in Ethnically and Culturally Diverse Sub-Populations in India: Gaps, Opportunities, and Future Directions

India is a large middle-income country and has surpassed China in overall population, comprising 20% of the global population (over 1.43 billion people). India is experiencing a major demographic shift in its aging population. Chronic diseases are common among older adults and can be persistent over the life course, lead to the onset of disability, and be costly. Among older adults in India, the existence of multiple comorbid chronic conditions (i.e., multimorbidity) is rapidly growing and represents a burgeoning public health burden. Prior research identified greater rates of multimorbidity (e.g., overweight/obesity diabetes, hypertension, cardiovascular disease, stroke, and malignancies) in minority populations in the United States (U.S.); however, limited studies have attempted to characterize multimorbidity among older adult sub-populations residing in India. To address this gap, we conducted a narrative review of studies on multimorbidity using the data from the Longitudinal Aging Study of India (LASI), the largest nationally representative longitudinal survey study of adults in India. Our definition of multimorbidity was the presence of more than two conditions in the same person. Our findings, based on 15 reviewed studies, aim to (1) characterize the definition and measurement of multimorbidity and to ascertain its prevalence in ethnically and culturally diverse sub-populations in India; (2) identify adverse outcomes associated with multimorbidity in the Indian adult population; and (3) identify gaps, opportunities, and future directions.

Harmonisation of later-life cognitive function across national contexts: results from the Harmonized Cognitive Assessment Protocols

BACKGROUND

The Harmonized Cognitive Assessment Protocol (HCAP) is an innovative instrument for cross-national comparisons of later-life cognitive function, yet its suitability across diverse populations is unknown. We aimed to harmonise general and domain-specific cognitive scores from HCAP studies across six countries, and evaluate reliability and criterion validity of the resulting harmonised scores.

METHODS

We statistically harmonised general and domain-specific cognitive function scores across publicly available HCAP partner studies in China, England, India, Mexico, South Africa, and the USA conducted between October, 2015 and January, 2020. Participants missing all cognitive test items in a given HCAP were excluded. We used an item banking approach that leveraged common cognitive test items across studies and tests that were unique to studies. We generated harmonised factor scores to represent a person's relative functioning on the latent factors of general cognitive function, memory, executive function, orientation, and language using confirmatory factor analysis. We evaluated the marginal reliability, or precision, of the factor scores using test information plots. Criterion validity of factor scores was assessed by regressing the scores on age, gender, and educational attainment in a multivariable analysis adjusted for these characteristics.

FINDINGS

We included 21 144 participants from the six HCAP studies of interest (11 480 women [54·3%] and 9664 [45·7%] men), with a median age of 69 years (IQR 64-76). Confirmatory factor analysis models of cognitive function in each country fit well: 31 (88·6%) of 35 models had adequate or good fit to the data (comparative fit index ≥0·90, root mean square error of approximation ≤0·08, and standardised root mean residual ≤0·08). Marginal reliability of the harmonised general cognitive function factor was high (>0·9) for 19 044 (90·1%) of 21 144 participant scores across the six countries. Marginal reliability of the harmonised factor was above 0·85 for 19 281 (91·2%) of 21 142 participant factor scores for memory, 7805 (41·0%) of 19 015 scores for executive function, 3446 (16·3%) of 21 103 scores for orientation, and 4329 (20·5%) of 21 113 scores for language. In each country, general cognitive function scores were lower with older age and higher with greater levels of educational attainment.

INTERPRETATION

We statistically harmonised cognitive function measures across six large population-based studies of cognitive ageing. These harmonised cognitive function scores empirically reflect comparable domains of cognitive function among older adults across the six countries, have high reliability, and are useful for population-based research. This work provides a foundation for international networks of researchers to make improved inferences and direct comparisons of cross-national associations of risk factors for cognitive outcomes in pooled analyses.

FUNDING

US National Institute on Aging.