A study on the sample representativeness of the Wisconsin Alzheimer’s Disease Research Center Clinical Core participants versus the Wisconsin state population

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Abstract Background Understanding how representative a research sample is compared to the population can help inform future recruitment planning, data analysis strategies, and interpretation of the generalizability of the findings. We compared the demographics, rural residence, neighborhood socioeconomic disadvantage, and vascular risk factors between the Wisconsin Alzheimer’s Disease Research Center (ADRC) Clinical Core participants versus the Wisconsin state adult population. Method The ADRC participant sample (n = 678) included all active participants as of November 30, 2021. The state population statistics were estimated using multiple national and state data sources. Differences between the sample versus the population were tested using the one‐sample z‐test, the one‐sample Wilcoxon signed rank test, the exact binomial test, and the exact Monte Carlo multinomial test. Except for age, comparisons were performed for two age groups: 45‐64 years and ≥ 65 years, separately. Result The ADRC participants are older than the state population. For each age group, compared to the state population, the ADRC participants include more women and greater proportions of Black and American Indians, have higher levels of educational attainment, have smaller percentages living in rural areas and more disadvantaged neighborhoods, and show lower vascular risks. The sample versus population differences are greater for the ≥ 65 years group (the group at higher risk for AD) than the 45‐64 years group for most metrics, however, are smaller for sex and neighborhood disadvantage. Conclusion The ADRC targets recruiting middle‐aged and older adults with dementia, mild cognitive impairment, or increased risk for AD. Thus, the participants are not a suitable sample for epidemiology studies on AD prevalence. Oversampling underrepresented racial groups would alleviate the lack of statistical power associated with small or unbalanced sample sizes and increase the precision in effect size estimates for studies on racial disparities. Future recruitment should endeavor to include participants from a broader range of educational backgrounds and more residents in rural areas and disadvantaged neighborhoods. These subpopulations have inequitable access to quality health care and are at greater risk. Properly representing them in research would allow conclusions to be generalizable to these subpopulations and support policy making to meet their needs.

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