Enhancing data quality for cross-national harmonization: Assessment of cognitive function in the CHARLS HCAP by language, literacy, and visual impairment

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Alzheimer’s disease and related dementias (ADRD) are a major global public health and policy challenge. The NIA has invested in addressing the global ADRD burden through funding the Harmonized Cognitive Assessment Protocol (HCAP) sub-studies of the US Health and Retirement and its International Partner Studies. The HCAP is an innovation that aims to allow, for the first time, comparable measurement of cognitive function among older adults around the world. The HCAP in the China Health and Retirement Longitudinal Study (CHARLS) was first deployed in Wave 4 of CHARLS in 2018 to participants aged ≥60 years. China is a large, diverse country with at least nine languages and seven dialects of Mandarin spoken amongst its population. Illiteracy (35.3% prevalence) and uncorrected visual impairment (18.3% prevalence) are also common in the older population. However, interview materials for the CHARLS HCAP were prepared and administered assuming fluency in spoken and written standard Mandarin and were not systematically adapted to account for illiteracy or visual impairment. If performance on a cognitive test item is affected by these extraneous features rather than a respondent’s true level of cognition, then differential item functioning (DIF) is said to be present for that cognitive test item. While DIF can lead to biased cognitive scores, we have tools that can, given assumptions, adjust for such DIF to improve measurement of cognition. The goal of this supplemental application is to decontaminate measurement differences in the CHARLS HCAP cognitive test battery due to spoken language or dialect, written literacy, and visual ability from true underlying levels of cognitive function. The parent R01 (R01AG070953) aims to statistically harmonize HCAP measures and test for DIF at the country-level across five different countries (US, Mexico, England, South Africa, and India). The present supplemental application is an extension of the statistical machinery and scientific scope of the parent grant. We propose to 1) identify and adjust for potential DIF in measurement of cognitive function in CHARLS HCAP due to language or dialect, literacy, and visual ability; and 2) Identify and adjust for potential DIF in measurement of cognitive function in prior waves of CHARLS (Waves 1, 2, 3), by language or dialect, literacy, and visual ability. After performing DIF analysis and adjusting cognitive scores as needed for DIF, we will examine whether the associations of each of age, sex, education, and urban/rural residence with DIF-adjusted cognitive scores will differ from the non-DIF-adjusted scores in ways that suggest reduction of bias due to language or dialect, illiteracy, and vision impairment in the DIF-adjusted scores. Successful completion of this proposed supplement will help improve the quality of existing CHARLS cognitive data, and will produce recommendations for the content, administration, and interviewer training for the cognitive test battery in future planned waves of CHARLS HCAP. We anticipate that this work will enable us to recommend additional information to collect alongside cognitive measures to enhance data quality and assist interpretations, such as objective measurement of language, literacy, and visual ability.