Exploring the structure of a neuropsychological battery across healthy elders and those with questionable dementia and Alzheimer's disease.

Abstract

An exploratory factor analysis (EFA) and a series of confirmatory factor analyses were conducted on 17 variables designed to assess different cognitive abilities in a sample of healthy older adults. In the EFA, four factors emerged corresponding to language, memory, processing speed, and fluid ability constructs. The results of the confirmatory factor analyses suggested that a five-factor model with an additional Attention factor improved the fit. The invariance of the five-factor model was examined across three groups-a group of cognitively-healthy older adults, a group of patients diagnosed with questionable dementia (QD), and a group of patients diagnosed with probable Alzheimer's Disease (AD). Results of the invariance analysis suggest that the model may have configural invariance across the three groups, but not metric invariance. Specifically, preliminary analyses suggest that the memory construct may represent something different in the QD and AD group as compared to the healthy elderly group, consistent with the underlying pathology in early AD. KeywordsAlzheimer's disease; questionable dementia; cognition; structural equation modeling; invariance Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by impairments in cognitive abilities and activities of daily living. Although normal aging is associated with age-related declines across a variety of cognitive abilities (e.g. Salthouse, in press), AD-related declines in functioning are different because the declines interfere with daily life. Questionable dementia (QD) is a categorization designed to characterize individuals who demonstrate mild cognitive impairment beyond what is expected by age and education but whose cognitive and/or functional impairment is not sufficient for the diagnosis of dementia.There is overwhelming evidence that there are changes in performance in tests of cognitive functioning across groups of older adults categorized as being either healthy, diagnosed with QD, or diagnosed with probable AD. Specifically, patients with QD and AD perform worse on memory and other tests designed to measure cognitive functions such as attention, language, and executive function than do cognitively-healthy older adults. Although it is clear that there are quantitative differences in the cognitive tests (i.e. demented patients perform worse), it is unclear whether there are consistent qualitative differences across these three diagnostic Correspondence to Yaakov Stern, 630 W 168 th St, New York, NY 10032, tel 212-342-1350, fax 212-342-1838 NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript groups. Qualitative differences refer to differences in relations among variables and differences in what the variables may be measuring. In this paper we used two techniques to address this question: invariance analyses, and comparison of the structure through separate exploratory factor analysis (EFA). Examining whether the structure of variables is the same (invariant) across groups is important beca...

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