Harmonizing late-life cognitive performance data across two population-based cohort studies: The Health and Retirement Study and National Health and Aging Trends Study.

INTRODUCTION: Harmonizing cognitive measures across population-based studies facilitates direct comparisons of cognitive decline despite differing study protocols.

METHODS: Cognitive performance data from 2012-2022 were harmonized across the Health and Retirement Study (HRS) and National Health and Aging Trends Study (NHATS). We compared baseline harmonized scores stratified by demographics and examined demographic and health risk factor associations with cognitive change using multi-level generalized linear models, contrasting results with those from a sum-of-word-recall measure.

RESULTS: Cross-sectionally, lower harmonized scores were associated with older age and less education. Longitudinally, greater cognitive decline measured by changes in harmonized scores correlated with older age, less education, underweight body mass index, low physical activity, hypertension, stroke, and diabetes. Associations were stronger for harmonized scores than for sum of word recall alone.

DISCUSSION: Harmonized scores effectively capture cognitive performance and decline, demonstrating stronger relationships with demographic and health factors than word recall scores alone.

HIGHLIGHTS: Statistical harmonization is a valuable tool for undertaking comparative analysis when data collection protocols differ.We derived a harmonized general cognitive performance factor score for the Health and Retirement Study (HRS) and National Health and Aging Trends Study (NHATS), two of the largest, nationally representative longitudinal samples of the middle-aged and older adult population in the United States.The factor score showed patterns of change across exposure groups consistent with prior literature, and it outperformed a simple sum score of immediate and delayed word recall tests.