Co-calibration of cognitive performance in the National Health and Aging Trends Study with the Health and Retirement Study's Harmonized Cognitive Assessment Protocol: Implications for dementia classification.

Large population-based studies are crucial for dementia research; yet variation in cognitive tests and dementia classification approaches can lead to inconsistent findings. We harmonized cognitive data from two nationally representative US studies of aging to facilitate comparisons. We examined 2016 data for individuals aged ≥70 years from the National Health and Aging Trends Study (NHATS) (n = 5696) and the Harmonized Cognitive Assessment Protocol (HCAP) of the Health and Retirement Study (HRS) (n = 2731). We derived factor scores for general cognitive performance in the NHATS cognitive test battery that were co-calibrated to the HRS-HCAP battery and identified cutpoints for dementia that returned the expected prevalence in each study. We evaluated diagnostic characteristics of the cutpoints against study-specific dementia algorithms with Area Under the Curve analysis. Study-specific algorithms yielded comparable dementia prevalence estimates: 10.8 % in NHATS and 11.1 % in HRS-HCAP. Co-calibrated scores showed similar distributions and had acceptable reliability, with similar dementia cutpoints. In both studies, sensitivity was higher among lower-educated (vs. higher educated) and non-White (vs. non-Hispanic White) groups. Co-calibrated populations with dementia in both studies had similar age and gender distributions but differed somewhat in education levels and race/ethnicity profiles. NHATS and HRS-HCAP both provide reliable cognitive function measures and dementia prevalence estimates for older Americans. Co-calibrated scores based on each study's cognitive test battery provide a valid and feasible approach for comparative US research. Better aligned algorithmic approaches across studies could strengthen opportunities for comparative studies of disparities in the US context using the co-calibration approach.