Cross-national harmonization of cognitive measures across HRS HCAP (USA) and LASI-DAD (India)

Harmonized cognitive performance in an older adult cohort of Vietnamese American immigrants: The VIP study

INTRODUCTION

Vietnamese Americans represent an understudied population with unique risk factors relevant to cognitive aging. The current study sought to model global cognition in the Vietnamese Insights into Cognitive Aging Program (VIP) study and harmonize ability estimates with the National Alzheimer's Coordinating Center (NACC) Uniform Data Set.

METHODS

Cognitive data from VIP (N = 548) and NACC (N = 15,923) were analyzed using item response theory. Seven common items were assessed for differential item functioning (DIF); items without salient DIF were used to harmonize the cognitive composite score across the two cohorts.

RESULTS

Although five of the seven common items showed evidence of DIF, the magnitude of this DIF was negligible, affecting the factor score estimates of only 12 (2.19%) VIP participants by more than one standard error.

DISCUSSION

Global cognitive functioning can be estimated in Vietnamese American immigrants with minimal bias and psychometrically matched to one of the largest studies of cognitive aging and dementia worldwide.

HIGHLIGHTS

This is the first known study to model cognition in older Vietnamese Americans. Global cognition was harmonized with minimal bias across two diverse cohorts. Differential item functioning was found in five of seven items, but the impact was not salient. Results create new opportunities to study health disparities in an underrepresented group.

Development and validation of a harmonized memory score for multicenter Alzheimer's disease and related dementia research

INTRODUCTION

List-learning tasks are important for characterizing memory in ADRD research, but the Uniform Data Set neuropsychological battery (UDS-NB) lacks a list-learning paradigm; thus, sites administer a range of tests. We developed a harmonized memory composite that incorporates UDS memory tests and multiple list-learning tasks.

METHODS

Item-banking confirmatory factor analysis was applied to develop a memory composite in a diagnostically heterogenous sample (n=5943) who completed the UDS-NB and one of five list-learning tasks. Construct validity was evaluated through associations with demographics, disease severity, cognitive tasks, brain volume, and plasma phosphorylated tau (p-tau181 and p-tau217). Test-retest reliability was assessed. Analyses were replicated in a racially/ethnically diverse cohort (n=1058).

RESULTS

Fit indices, loadings, distributions, and test-retest reliability were adequate. Expected associations with demographics and clinical measures within development and validation cohorts supported validity.

DISCUSSION

This composite enables researchers to incorporate multiple list-learning tasks with other UDS measures to create a single metric.

Development of a refined harmonization approach for longitudinal cognitive data in people with HIV

OBJECTIVES

The aim of this study was to develop a refined method for harmonizing longitudinal cognitive data across several large-scale studies in people with HIV (PWH), in whom cognitive complications are common and heterogeneous in presentation.

STUDY DESIGN AND SETTING

We developed a refined method for harmonizing longitudinal cognitive data across five large-scale studies in PWH that used different cognitive batteries with only some overlapping tests-Women's Interagency HIV Study (WIHS), Multicenter AIDS Cohort Study, CNS HIV Antiretroviral Therapy Effects Research (CHARTER), National NeuroAIDS Tissue Consortium, and the HIV Neurobehavioral Research Program. Traditional data harmonization methods using latent variable models focus on cross-sectional data and require the presence of common cognitive tests to serve as "linking" assessments. However, the absence of such common tests for certain cognitive domains can preclude the direct application of these traditional techniques. To address these challenges, we developed a harmonization method that leveraged a second-order factor model, which capitalized on the structural relationships among cognitive domains.

RESULTS

Our approach yielded harmonized cognitive domain scores that are demographically consistent across different cohorts and exhibit strong correlations with the raw or log transformed (eg, timed outcomes) cognitive test scores. These harmonized scores accurately reflected variations according to age, educational status, and other demographic factors, while preserving participants' longitudinal cognitive trajectories.

CONCLUSION

Our harmonization methods are essential for future analyses of large-scale, retrospective data to understand the heterogeneity in cognitive complications in PWH. These methods can be applied to harmonize new datasets with similar measures.

A study evaluation framework for measuring cognition. Lessons learned in cross-national contexts from four English-speaking aging cohorts

The Harmonized Cognitive Assessment Protocol (HCAP) is a detailed battery assessing cognition among older people used by studies across the world. Data harmonization is a key priority for HCAP studies. We used a mixed-methods approach using established theories from the existing literature detailing the methodologies of longitudinal studies and from the implementation of HCAP in four English-speaking studies adopting the same protocol. Through a detailed investigation involving the English Longitudinal Study of Ageing (ELSA), the Health and Retirement Study (HRS), The Irish Longitudinal Study on Ageing (TILDA), and the Northern Ireland Cohort for the Longitudinal Study of Ageing (NICOLA), we identified 60 factors contributing to the development of a conceptual framework for the evaluation and implementation of HCAP. We present this framework and a prototype checklist as a tool for providing a transparent and structured approach to improve data quality, cross-country comparability and for identifying, mitigating, and monitoring sources of bias. The framework consisting of four broad headings: (1) Organisation and design, (2) Competency of personnel and systems, (3) Implementation and outputs, and (4) Feedback and communication. Studies seeking to harmonize results in cross-national contexts should give operational aspects of fieldwork careful consideration as part of the harmonization process.

Estimating dementia prevalence using remote diagnoses and algorithmic modelling: a population-based study of a rural region in South Africa

BACKGROUND

Dementia is a leading cause of global death and disability. High-quality data describing dementia prevalence and burden remain scarce in sub-Saharan Africa. Health and Aging in Africa: A Longitudinal Study in South Africa (HAALSI) fills evidence gaps with longitudinal data on cognition, biomarkers, and everyday function in a population-based cohort of Black South Africans, aged 40 years and older, in a rural subdistrict. This study uses consensus diagnoses and prediction algorithms to estimate dementia prevalence.

METHODS

Data were from eligible HAALSI Wave 2 respondents aged 50 years or older (n=3662) and were collected between September, 2019, and January, 2020. An enriched sub-cohort (ie, including a high proportion of individuals with cognitive impairment; n=632) completed a battery of rigorous neuropsychological and clinical assessments and received expert classification of cognitively unimpaired, mild cognitive impairment, or dementia. Logistic regression was used to predict dementia status within the sub-cohort using predictor variables from the parent HAALSI wave. Coefficients were applied to the parent cohort to obtain dementia probability scores and calculate dementia prevalence. Optimal probability cut points to classify individual cases were selected for each model.

FINDINGS

When the sub-cohort was reweighted to reflect the full HAALSI population, the estimated prevalence of dementia was 18% (95% CI 15-22), with steep age gradients. Four models of increasing complexity showed good discrimination between dementia and non-dementia (area under receiver operating characteristic curves 0·78-0·84; classification accuracy 74-81%). Model-based dementia prevalence estimates aligned closely with weighted prevalence; model performance was consistent in cross-validated datasets.

INTERPRETATION

HAALSI is among the first studies to use algorithmic methods to describe dementia prevalence in a population-based sample in South Africa. These efforts could provide a foundation to expand understanding of dementia epidemiology in a region of the world experiencing rapid population ageing.

FUNDING

National Institute on Aging.

Age differences in the change in cognition after stroke

OBJECTIVE

To compare changes in cognitive trajectories after stroke between younger (18-64) and older (65+) adults, accounting for pre-stroke cognitive trajectories.

MATERIALS AND METHODS

Pooled cohort study using individual participant data from 3 US cohorts (1971-2019), the Atherosclerosis Risk In Communities Study (ARIC), Framingham Offspring Study (FOS), and REasons for Geographic And Racial Differences in Stroke Study (REGARDS). Linear mixed effect models evaluated the association between age and the initial change (intercept) and rate of change (slope) in cognition after compared to before stroke. Outcomes were global cognition (primary), memory and executive function.

RESULTS

We included 1,292 participants with stroke; 197 younger (47.2 % female, 32.5 % Black race) and 1,095 older (50.2 % female, 46.4 % Black race). Median (IQR) age at stroke was 59.7 (56.6-61.7) (younger group) and 75.2 (70.5-80.2) years (older group). Compared to the young, older participants had greater declines in global cognition (-1.69 point [95 % CI, -2.82 to -0.55] greater), memory (-1.05 point [95 % CI, -1.92 to -0.17] greater), and executive function (-3.72 point [95 % CI, -5.23 to -2.21] greater) initially after stroke. Older age was associated with faster declines in global cognition (-0.18 points per year [95 % CI, -0.36 to -0.01] faster) and executive function (-0.16 [95 % CI, -0.26 to -0.06] points per year for every 10 years of higher age), but not memory (-0.006 [95 % CI, -0.15 to 0.14]), after compared to before stroke.

CONCLUSION

Older age was associated with greater post-stroke cognitive declines, accounting for differences in pre-stroke cognitive trajectories between the old and the young.

Type II diabetes and cognitive function among older adults in India and China-results from Harmonized Cognitive Assessment Protocol studies

Objective

Type II diabetes is a recognized risk factor of declining cognitive function in high-income countries. However, there is limited research on this association across low- and middle-income countries. We aimed to examine and compare the relationship between type II diabetes and cognition amongst adults aged 60 years and older for two of the largest LMICs: India and China.

Methods

Cross-sectional data was analyzed from population-based Harmonized Cognitive Assessment Protocols studies in India (n = 4,062) and China (n = 9,741). Multivariable-adjusted linear regression models examined the relationship between diabetes (self-reported or biomarker HbA1c ≥6.5%) and general cognition. Interaction testing assessed effect modification based on urban versus rural residence and educational attainment.

Results

Type II diabetes was not associated with general cognitive scores in India or China in fully adjusted models. Interaction testing revealed a positive association in rural but not urban residences in India, however this was not seen in China. Both countries showed effect modification by education attainment. In India, diabetes was associated with higher average cognitive scores among those with none or early childhood education, while the relationship was null among those with at least an upper secondary education. In China, diabetes was inversely related to average cognitive scores among those with less than lower secondary education, while the relationship was null among the remainder of the study sample.

Conclusion

The type II diabetes and cognitive function association in India and China differs from that observed in high-income countries. These findings suggest epidemiologic and nutrition transition variations. In India, health care access, urbanization and social differences between urban and rural areas may influence this relationship. In both countries, epidemiologic and nutrition patterns may adversely impact individuals from socially and financially vulnerable populations with less than lower secondary education. Longitudinal research using harmonized cognitive scores is encouraged to further investigate these findings.

Lifetime occupational skill and later-life cognitive function among older adults in the United States, Mexico, India, and South Africa

INTRODUCTION

We conducted a cross-national comparison of the association between main lifetime occupational skills and later-life cognitive function across four economically and socially distinct countries.

METHODS

Data were from population-based studies of aging and their Harmonized Cognitive Assessment Protocols (HCAPs) in the US, South Africa, India, and Mexico (N = 10,037; Age range: 50 to 105 years; 2016 to 2020). Main lifetime occupational skill was classified according to the International Standard Classification of Occupations. Weighted, adjusted regression models estimated pooled and country-specific associations between main lifetime occupational skill and later-life general cognitive function in men and women.

RESULTS

We observed positive gradients between occupational skill and later-life cognitive function for men and women in the US and Mexico, a positive gradient for women but not men in India, and no association for men or women in South Africa.

DISCUSSION

Main lifetime occupations may be a source of later-life cognitive reserve, with cross-national heterogeneity in this association.

HIGHLIGHTS

No studies have examined cross-national differences in the association of occupational skill with cognition. We used data from Harmonized Cognitive Assessment Protocols in the US, Mexico, India, and South Africa. The association of occupational skill with cognitive function varies by country and gender.

How Does Tobacco Use Affect the Cognition of Older Adults? A Propensity Score Matching Analysis Based on a Large-Scale Survey

INTRODUCTION

Tobacco is a well-established risk factor for cancer, but its association with other morbidities needs consideration. The low-income and middle-income countries (LMICs) with unprecedented demographic transformation lack evidence on tobacco use and its impact on cognitive health.

AIMS AND METHODS

Using a propensity score matching approach, we utilized data from the Longitudinal Ageing Study of India. Study employed 1:1 nearest neighbor matching with the replacement methodology. We estimated the odds of the poor cognitive score and tobacco use among older adults based on five different models for ever tobacco user, former tobacco user, current tobacco user, current smokers, and current smokeless tobacco users with reference to never tobacco users.

RESULTS

The estimated average treatment effect for the treated and the untreated group has shown a higher likelihood of cognitive decline among ever (OR -0.26; 95%CI -0.43 to -0.09), current (OR -0.28; 95%CI -0.45 to -0.10), and former (OR -0.53; 95%CI -0.87 to -0.19) tobacco users compared to never tobacco users. The finding further suggests the odds of lower cognitive scores among older adults who were smokers (OR -0.53; 95%CI -0.87 to -0.19) and smokeless tobacco users (OR -0.22; 95%CI -0.43 to -0.01) as compared to never tobacco users.

CONCLUSIONS

Interventions designed to prevent the incidence of cognitive impairment should focus on limiting the use of tobacco. Strategies under the tobacco-free generation initiative should be amplified in order to prevent future generations from productivity loss, premature ageing and to promote healthy aging.

IMPLICATIONS

Evidence of a definitive association between tobacco consumption and cognition among older adults is sporadic in LMICs. Though tobacco is a risk factor for various diseases including cancer, the extent of its impact on cognitive health among the older population is limited. This study contributes to the existing literature by highlighting poor cognitive outcomes among older adults who smoke tobacco and/or consume smokeless tobacco as compared to never-tobacco users. Our findings emphasize the need to accelerate programmes related to tobacco-free generation in LMICs to reach a higher quality of life and healthy aging in pursuit of achieving the sustainable development goal of "good health and well-being."

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

INTRODUCTION

We compared gender disparities in later-life memory, overall and by education, in India and the United States (US).

METHODS

Data (N = 7443) were from harmonized cognitive assessment protocols (HCAPs) in the Longitudinal Aging Study of India-Diagnostic Assessment of Dementia (LASI-DAD; N = 4096; 2017-19) and US Health and Retirement Study HCAP (HRS-HCAP; N = 3347; 2016-17). We derived harmonized memory factors from each study using confirmatory factor analysis. We used multivariable-adjusted linear regression to compare gender disparities in memory function between countries, overall and by education.

RESULTS

In the United States, older women had better memory than older men (0.28 SD-unit difference; 95% CI: 0.22, 0.35). In India, older women had worse memory than older men (-0.15 SD-unit difference; 95% CI: -0.20, -0.10), which attenuated with increasing education and literacy.

CONCLUSION

We observed gender disparities in memory in India that were not present in the United States, and which dissipated with education and literacy.

Speech and language markers of neurodegeneration: a call for global equity

In the field of neurodegeneration, speech and language assessments are useful for diagnosing aphasic syndromes and for characterizing other disorders. As a complement to classic tests, scalable and low-cost digital tools can capture relevant anomalies automatically, potentially supporting the quest for globally equitable markers of brain health. However, this promise remains unfulfilled due to limited linguistic diversity in scientific works and clinical instruments. Here we argue for cross-linguistic research as a core strategy to counter this problem. First, we survey the contributions of linguistic assessments in the study of primary progressive aphasia and the three most prevalent neurodegenerative disorders worldwide-Alzheimer's disease, Parkinson's disease, and behavioural variant frontotemporal dementia. Second, we address two forms of linguistic unfairness in the literature: the neglect of most of the world's 7000 languages and the preponderance of English-speaking cohorts. Third, we review studies showing that linguistic dysfunctions in a given disorder may vary depending on the patient's language and that English speakers offer a suboptimal benchmark for other language groups. Finally, we highlight different approaches, tools and initiatives for cross-linguistic research, identifying core challenges for their deployment. Overall, we seek to inspire timely actions to counter a looming source of inequity in behavioural neurology.

Assessing cognitive function in longitudinal studies of ageing worldwide: some practical considerations

Over 55 million people live with dementia worldwide. With 40% of modifiable risk factors estimated to contribute to dementia, the potential for prevention is high, and preventive measures, at an early stage of cognitive decline, are likely to positively influence future dementia trends. Countries need reliable health data and adequate measurement tools to quantify, monitor and track early changes in cognitive capacity in the general population. Many cognitive tests exist; however, there is no consensus to date about which instruments should be employed, and important variations in measurement have been observed. In this narrative review, we present a number of cognitive tests that have been used in nationally representative population-based longitudinal studies of ageing. Longitudinal panel studies of ageing represent critical platforms towards capturing the process of cognitive ageing and understanding associated risk and protective factors. We highlight optimal measures for use at a population level and for cross-country comparisons, taking into consideration instrument reliability, validity, duration, ease of administration, costs, literacy and numeracy requirements, adaptability to sensory and fine motor impairments and portability to different cultural and linguistic milieux. Drawing upon the strengths and limitations of each of these tests, and the experience gained and lessons learnt from conducting a nationally representative study of ageing, we indicate a comprehensive battery of tests for the assessment of cognitive capacity, designed to facilitate its standardised operationalisation worldwide.

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.

Negative wealth shocks in later life and subsequent cognitive function in older adults in China, England, Mexico, and the USA, 2012-18: a population-based, cross-nationally harmonised, longitudinal study

BACKGROUND

Household wealth is positively related to cognitive health outcomes in later life. However, the association between negative wealth shocks and cognitive function in later life, and whether this association might differ across countries at different levels of economic development, is unclear. We aimed to investigate whether negative wealth shocks in later life are associated with cognitive function in older adults in China, England, Mexico, and the USA, and whether this association is modified by country income level.

METHODS

For this population-based, cross-nationally harmonised, longitudinal study, data were analysed from core interviews of the population-based US Health and Retirement Study (2012 and 2016) and its partner studies in China (the China Health and Retirement Longitudinal Study; 2015 and 2018), England (the English Longitudinal Study of Ageing; 2012 and 2016), and Mexico (Mexican Health and Aging Study; 2012 and 2015-16), and their respective Harmonized Cognitive Assessment Protocols (HCAPs). Negative wealth shocks over the follow-up periods of the respective cohorts were defined in two ways: an extreme loss of 75% or greater from the baseline amount of wealth, and a decline in within-population wealth quintile rank. The primary outcome was the harmonised general cognitive function (GCF) factor score, which was constructed with factor analysis on the HCAP neuropsychological assessments of memory, orientation, attention, executive function, and verbal fluency performance (mean 0; SD 1). We used sampling-weighted, multivariable-adjusted linear models to examine associations.

FINDINGS

Data from 9465 participants were included in this analysis: 3796 from China, 1184 from England, 1193 from Mexico, and 3292 from the USA. The mean baseline age of participants was 68·5 (SD 5·4) years in China (49·8% women), 72·0 (7·0) years in England (54·6% women), 70·6 (6·8) years in Mexico (55·1% women), and 72·7 (7·5) years in the USA (60·4% women). A wealth loss of 75% or greater was negatively associated with subsequent cognitive function in the USA (β -0·16 SD units; 95% CI -0·29 to -0·04) and China (-0·14; -0·21 to -0·07), but not in England (-0·01; -0·24 to 0·22) or Mexico (-0·11; -0·24 to 0·03). Similarly, within-population wealth quintile rank declines were negatively associated with subsequent cognitive function in the USA (β -0·07 per quintile rank decline; 95% CI -0·11 to -0·03) and China (β -0·07; -0·09 to -0·04), but not in England (-0·05; -0·11 to 0·01) or Mexico (-0·03; -0·07 to 0·01).

INTERPRETATION

The impact of wealth shocks in later life on subsequent lower level of cognitive function of older adults in China, England, Mexico, and the USA differed across macro-level socioeconomic structures. These findings suggest that government policies and social safety nets in countries with different levels of economic development might have a role in protecting older adults from adverse health effects of wealth losses in later life.

FUNDING

US National Institute on Aging, US National Institutes of Health.

Propensity Scores in Health Disparities Research: The Example of Cognitive Aging and the Hispanic Paradox

BACKGROUND

Individuals of Mexican ancestry in the United States experience substantial socioeconomic disadvantages compared with non-Hispanic white individuals; however, some studies show these groups have similar dementia risk. Evaluating whether migration selection factors (e.g., education) associated with risk of Alzheimer disease and related dementia (ADRD) explain this paradoxical finding presents statistical challenges. Intercorrelation of risk factors, common with social determinants, could make certain covariate patterns very likely or unlikely to occur for particular groups, which complicates their comparison. Propensity score (PS) methods could be leveraged here to diagnose nonoverlap and help balance exposure groups.

METHODS

We compare conventional and PS-based methods to examine differences in cognitive trajectories between foreign-born Mexican American, US-born Mexican American, and US-born non-Hispanic white individuals in the Health and Retirement Study (1994-2018). We examined cognition using a global measure. We estimated trajectories of cognitive decline from linear mixed models adjusted for migration selection factors also associated with ADRD risk conventionally or with inverse probability weighting. We also employed PS trimming and match weighting.

RESULTS

In the full sample, where PS overlap was poor, unadjusted analyses showed both Mexican ancestry groups had worse baseline cognitive scores but similar or slower rates of decline compared with non-Hispanic white adults; adjusted findings were similar, regardless of method. Focusing analyses on populations where PS overlap was improved (PS trimming and match weighting) did not alter conclusions.

CONCLUSIONS

Attempting to equalize groups on migration selection and ADRD risk factors did not explain paradoxical findings for Mexican ancestry groups in our study.

Memory and language cognitive data harmonization across the United States and Mexico

INTRODUCTION

We used cultural neuropsychology-informed procedures to derive and validate harmonized scores representing memory and language across population-based studies in the United States and Mexico.

METHODS

Data were from the Health and Retirement Study Harmonized Cognitive Assessment Protocol (HRS-HCAP) and the Mexican Health and Aging Study (MHAS) Ancillary Study on Cognitive Aging (Mex-Cog). We statistically co-calibrated memory and language domains and performed differential item functioning (DIF) analysis using a cultural neuropsychological approach. We examined relationships among harmonized scores, age, and education.

RESULTS

We included 3170 participants from the HRS-HCAP (Mage = 76.6 [standard deviation (SD): 7.5], 60% female) and 2042 participants from the Mex-Cog (Mage = 68.1 [SD: 9.0], 59% female). Five of seven memory items and one of twelve language items demonstrated DIF by study. Harmonized memory and language scores showed expected associations with age and education.

DISCUSSION

A cultural neuropsychological approach to harmonization facilitates the generation of harmonized measures of memory and language function in cross-national studies.

HIGHLIGHTS

We harmonized memory and language scores across studies in the United States and Mexico.A cultural neuropsychological approach to data harmonization was used.Harmonized scores showed minimal measurement differences between cohorts.Future work can use these harmonized scores for cross-national studies of Alzheimer's disease and related dementias.

Harmonization of Later-Life Cognitive Function Across National Contexts: Results from the Harmonized Cognitive Assessment Protocols (HCAPs)

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 harmonize general and domain-specific cognitive scores from HCAPs across six countries, and evaluate precision and criterion validity of the resulting harmonized scores.

Methods

We statistically harmonized general and domain-specific cognitive function across the six publicly available HCAP partner studies in the United States, England, India, Mexico, China, and South Africa (N=21,141). We used an item banking approach that leveraged common cognitive test items across studies and tests that were unique to studies, as identified by a multidisciplinary expert panel. We generated harmonized factor scores for general and domain- specific cognitive function using serially estimated graded-response item response theory (IRT) models. We evaluated precision of the factor scores using test information plots and criterion validity using age, gender, and educational attainment.

Findings

IRT models of cognitive function in each country fit well. We compared measurement reliability of the harmonized general cognitive function factor across each cohort using test information plots; marginal reliability was high (r> 0·90) for 93% of respondents across six countries. In each country, general cognitive function scores were lower with older ages and higher with greater levels of educational attainment.

Interpretation

We statistically harmonized cognitive function measures across six large, population-based studies of cognitive aging in the US, England, India, Mexico, China, and South Africa. Precision of the estimated scores was excellent. This work provides a foundation for international networks of researchers to make stronger inferences and direct comparisons of cross-national associations of risk factors for cognitive outcomes.

Funding

National Institute on Aging (R01 AG070953, R01 AG030153, R01 AG051125, U01 AG058499; U24 AG065182; R01AG051158).

Alzheimer's disease genetic risk and cognitive reserve in relationship to long-term cognitive trajectories among cognitively normal individuals

BACKGROUND

Both Alzheimer's disease (AD) genetic risk factors and indices of cognitive reserve (CR) influence risk of cognitive decline, but it remains unclear whether they interact. This study examined whether a CR index score modifies the relationship between AD genetic risk factors and long-term cognitive trajectories in a large sample of individuals with normal cognition.

METHODS

Analyses used data from the Preclinical AD Consortium, including harmonized data from 5 longitudinal cohort studies. Participants were cognitively normal at baseline (M baseline age = 64 years, 59% female) and underwent 10 years of follow-up, on average. AD genetic risk was measured by (i) apolipoprotein-E (APOE) genetic status (APOE-ε2 and APOE-ε4 vs. APOE-ε3; N = 1819) and (ii) AD polygenic risk scores (AD-PRS; N = 1175). A CR index was calculated by combining years of education and literacy scores. Longitudinal cognitive performance was measured by harmonized factor scores for global cognition, episodic memory, and executive function.

RESULTS

In mixed-effects models, higher CR index scores were associated with better baseline cognitive performance for all cognitive outcomes. APOE-ε4 genotype and AD-PRS that included the APOE region (AD-PRSAPOE) were associated with declines in all cognitive domains, whereas AD-PRS that excluded the APOE region (AD-PRSw/oAPOE) was associated with declines in executive function and global cognition, but not memory. There were significant 3-way CR index score × APOE-ε4 × time interactions for the global (p = 0.04, effect size = 0.16) and memory scores (p = 0.01, effect size = 0.22), indicating the negative effect of APOE-ε4 genotype on global and episodic memory score change was attenuated among individuals with higher CR index scores. In contrast, levels of CR did not attenuate APOE-ε4-related declines in executive function or declines associated with higher AD-PRS. APOE-ε2 genotype was unrelated to cognition.

CONCLUSIONS

These results suggest that APOE-ε4 and non-APOE-ε4 AD polygenic risk are independently associated with global cognitive and executive function declines among individuals with normal cognition at baseline, but only APOE-ε4 is associated with declines in episodic memory. Importantly, higher levels of CR may mitigate APOE-ε4-related declines in some cognitive domains. Future research is needed to address study limitations, including generalizability due to cohort demographic characteristics.

Harmonizing Ethno-Regionally Diverse Datasets to Advance the Global Epidemiology of Dementia

Understanding dementia and cognitive impairment is a global effort needing data from multiple sources across diverse ethno-regional groups. Methodological heterogeneity means that these data often require harmonization to make them comparable before analysis. We discuss the benefits and challenges of harmonization, both retrospective and prospective, broadly and with a focus on data types that require particular sorts of approaches, including neuropsychological test scores and neuroimaging data. Throughout our discussion, we illustrate general principles and give examples of specific approaches in the context of contemporary research in dementia and cognitive impairment from around the world.

Statistical harmonization of everyday functioning and dementia-related behavioral measures across nine surveys and trials

Introduction

Efforts to harmonize measures of everyday function and dementia-related behaviors are needed to synthesize across studies in dementia research. There have been some psychometric attempts to harmonize everyday function for secondary analysis, but far less for dementia-related behaviors.

Methods

Statistical co-calibration was performed to generate factor scores representing everyday function and dementia-related behaviors for participants with dementia. We evaluated convergent criterion validity of factor scores and mapped the scores onto established clinical instruments.

Results

Factor analyses of included items fit well to available data. Harmonized factors showed expected associations with the Global Clinical Dementia Rating (CDR) score, with greater impairment (higher Global CDR score) corresponding to higher (more severe) levels on factor scores.

Discussion

We used large, well-characterized samples to derive harmonized factors representing everyday functions and dementia-related behaviors. These harmonized factors can be used to tackle questions about dementia phenotypes which require either large samples or unique subpopulations.

Neuropsychological Assessment of Older Adults in Nepal for Population-Based Dementia Ascertainment: Needs, Challenges, and Opportunities

The population of Nepal is rapidly aging, as in other low and middle-income countries, and the number of individuals living with Alzheimer's Disease and related dementias (ADRD) is expected to increase. However, information about the neuropsychological assessment of ADRD in Nepal is lacking. We first aimed to examine the needs, challenges, and opportunities associated with the neuropsychological assessment of older adults in Nepal for population-based ADRD ascertainment. Second, we introduce the Chitwan Valley Family Study-Study of Cognition and Aging in Nepal (CVFS-SCAN), which is poised to address these needs, and its collaboration with the Harmonized Cognitive Assessment Protocol (HCAP) international network. We reviewed the existing literature on the prevalence, risk factors, available neuropsychological assessment instruments, and sociocultural factors that may influence the neuropsychological assessment of older adults for ADRD ascertainment in Nepal. Our review revealed no existing population-based data on the prevalence of ADRD in Nepal. Very few studies have utilized formal cognitive assessment instruments for ADRD assessment, and there have been no comprehensive neuropsychological assessment instruments that have been validated for the assessment of ADRD in Nepal. We describe how the CVFS-SCAN study will address this need through careful adaptation of the HCAP instrument. We conclude that the development of culturally appropriate neuropsychological assessment instruments is urgently needed for the population-based assessment of ADRD in Nepal. The CVFS-SCAN is designed to address this need and will contribute to the growth of global and equitable neuropsychology and to the science of ADRD in low- and middle-income countries.

A guide for researchers seeking training in retrospective data harmonization for population neuroscience studies of Alzheimer's disease and related dementias

Due to needs surrounding rigor and reproducibility, subgroup specific disease knowledge, and questions of external validity, data harmonization is an essential tool in population neuroscience of Alzheimer's disease and related dementias (ADRD). Systematic harmonization of data elements is necessary to pool information from heterogeneous samples, and such pooling allows more expansive evaluations of health disparities, more precise effect estimates, and more opportunities to discover effective prevention or treatment strategies. The key goal of this Tutorial in Population Neuroimaging Curriculum, Instruction, and Pedagogy article is to guide researchers in creating a customized population neuroscience of ADRD harmonization training plan to fit their needs or those of their mentees. We provide brief guidance for retrospective data harmonization of multiple data types in this area, including: (1) clinical and demographic, (2) neuropsychological, and (3) neuroimaging data. Core competencies and skills are reviewed, and resources are provided to fill gaps in training as well as data needs. We close with an example study in which harmonization is a critical tool. While several aspects of this tutorial focus specifically on ADRD, the concepts and resources are likely to benefit population neuroscientists working in a range of research areas.