Coordinated analysis of age, sex, and education effects on change in MMSE scores

Abstract

Objectives: We describe and compare the expected performance trajectories of older adults on the Mini-Mental Status Examination (MMSE) across six independent studies from four countries in the context of a collaborative network of longitudinal studies of aging. A coordinated analysis approach is used to compare patterns of change conditional on sample composition differences related to age, sex, and education. Such coordination accelerates evaluation of particular hypotheses. In particular, we focus on the effect of educational attainment on cognitive decline.

Method: Regular and Tobit mixed models were fit to MMSE scores from each study separately. The effects of age, sex, and education were examined based on more than one centering point.

Results: Findings were relatively consistent across studies. On average, MMSE scores were lower for older individuals and declined over time. Education predicted MMSE score, but, with two exceptions, was not associated with decline in MMSE over time.

Conclusion: A straightforward association between educational attainment and rate of cognitive decline was not supported. Thoughtful consideration is needed when synthesizing evidence across studies, as methodologies adopted and sample characteristics, such as educational attainment, invariably differ.

Figure 1.

Education distribution (%) by study. Note. Gerontological and Geriatric Population Studies in Gothenburg, Sweden [H-70] and Swedish Adoption/Twin Study of Aging [SATSA]: 60% completed elementary school or less and 40% completed more than elementary school. CLS = Canberra Longitudinal Study; HOPE = Healthy Older Person Edinburgh; LASA = Longitudinal Aging Study Amsterdam; OCTO-Twin = Origins of Variance in the Oldest-Old.

Figure 2.

Meta-analysis using estimated age-distributed between-person (BP) differences (education) and within-person (WP) change (education × time) results for six studies. (Top panel) Educational attainment intercepts. (Bottom panel) Education × Time. Note. Estimates have been standardized to account for sample size heterogeneity. Panel 2 uses nondemented estimates for change in educational attainment in the OCTO-Twin study. CLS = Canberra Longitudinal Study; HOPE = Healthy Older Person Edinburgh; H-70 = Gerontological and Geriatric Population Studies in Gothenburg, Sweden; LASA = Longitudinal Aging Study Amsterdam; OCTO-Twin = Origins of Variance in the Oldest-Old; SATSA = Swedish Adoption/Twin Study of Aging.

Figure 3.

Predicted Mini-Mental Status Examination (MMSE) scores over time for a hypothetical man enrolling at the median age and years of education for each study. Predicted scores for Origins of Variance of the Oldest Old (OCTO-Twin) including and excluding (OCTOTwin_NDever) individuals diagnosed with dementia. CLS = Canberra Longitudinal Study; HOPE = Healthy Older Person Edinburgh; H-70 = Gerontological and Geriatric Population Studies in Gothenburg, Sweden; LASA = Longitudinal Aging Study Amsterdam; SATSA = Swedish Adoption/Twin Study of Aging.

Figure 4.

Scatterplots of years of formal education by individual fitted linear slope for each study and for Octogenarian Twins including and excluding individuals diagnosed with dementia. CLS = Canberra Longitudinal Study; HOPE = Healthy Older Person Edinburgh; LASA = Longitudinal Aging Study Amsterdam; OCTO-Twin = Origins of Variance in the Oldest-Old; SATSA = Swedish Adoption/Twin Study of Aging.