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Abstract
Objective: To re-examine proposed models of cognitive test performance that concluded separate factor structures were required for people with Alzheimer disease (AD) and older adults without dementia.
Methods: Five models of cognitive test performance were compared using multistep confirmatory factor analysis in 115 individuals with autopsy-confirmed AD and 191 research participants without clinical dementia from longitudinal studies at the Washington University AD Research Center. The models were then cross-validated using independent samples of 323 people with clinically diagnosed dementia of the Alzheimer type and 212 cognitively healthy older adults.
Results: After controlling for Alzheimer-specific changes in episodic memory, performance on the battery of tests used here was best represented in people both with and without dementia by a single model of one general factor and three specific factors (verbal memory, visuospatial ability, and working memory). Performance by people with dementia was lower on the general factor than it was by those without dementia. Larger variances associated with the specific factors in the group with dementia indicated greater individual differences in the pattern of cognitive deficits in the stage of AD.
Conclusions: A hybrid model of general and specific cognitive domains simplifies cognitive research by allowing direct comparison of normal aging and Alzheimer disease performance. The presence of a general factor maximizes detection of the dementia, whereas the specific factors reveal the heterogeneity of dementia’s associated cognitive deficits.
GLOSSARY: AD = Alzheimer disease; BD = Block Design; BNT = Boston Naming Test; BVRT = Benton Visual Retention Test; CDR = Clinical Dementia Rating; CFA = confirmatory factor analysis; CFI = comparative fit index; DAT = dementia of the Alzheimer type; DS-B = Digit Span Backward; DS-F = Digit Span Forward; DSym = Digit Symbol; INFO = information; LBs = Lewy bodies; LM = Logical Memory; MC = Mental Control; NIA = National Institute on Aging; PA = Paired Associate Learning; RMSEA = root mean square error of approximation; TOI = tests of invariance; TRA = Trailmaking A; WF = Word Fluency.
Footnotes
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Supported by National Institute on Aging grants P01 AG03991, P50 AG05681, and K08 AG20764; American Federation for Aging Research; and gifts from the Alan A. and Edith L. Wolff Charitable Trust.
Disclosure: The authors report no disclosures.
Received May 13, 2008. Accepted in final form August 20, 2008.
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