Purpose The Modified Mini-Mental State Examination (3MS) is used in research settings to screen for deficits in cognitive function among the elderly. Traditional scoring and item response theory (IRT) require tests to be unidimensional, where all the items measure one underlying trait. If the items on a test are not unidimensional it would be inappropriate to use a global summary score; several domain-specific scores would be more appropriate.
Methods We analyzed baseline 3MS responses from the Canadian Study of Health and Aging (CSHA), a prospective cohort study of elderly individuals (N = 8,121). We assessed the dimensionality of the 3MS with confirmatory factor analysis (CFA). We tested three structural models: 1) single factor model, 2) six orthogonal factors model, and 3) second order model with a general factor. We used Mplus to fit the hypothesized structural models. We compared goodness-of-fit statistics (χ2, CFI, TLI, and RMSEA). We assessed factorial invariance—whether factor relationships are the same in two different samples—in English-speaking (N = 6,579) and French-speaking (N = 1,542) subjects. Summary of
Results The second order model with a general factor fit the data better than the other two models tested. The general cognitive ability factor accounted for 52% of the variance. A χ2 global test of factorial invariance indicated no significant worsening in model fit when loadings for English- and French-speaking subjects were constrained to be equal. Loadings estimated separately in the two groups were very similar.
Conclusions Our analyses suggest that the 3MS can be conceptualized as a unidimensional test. The use of summary or IRT scores is thus not inappropriate. We found the structure of the 3MS to be equivalent in both the English- and French-administered versions, so the relationships between items and factors do not appear to be sample-dependent.
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