Intraindividual variability among cognitive domains may predict dementia independently of interindividual differences in cognition. A multidomain cognitive battery was administered to 2305 older adult women (mean age 74 years) enrolled in an ancillary study of the Women’s Health Initiative. Women were evaluated annually for probable dementia and mild cognitive impairment (MCI) for an average of 5.3 years using a standardized protocol. Proportional hazards regression showed that lower baseline domain-specific cognitive scores significantly predicted MCI ( ), probable dementia ( ), and MCI or probable dementia combined ( ) and that verbal and figural memory predicted each outcome independently of all other cognitive domains. The baseline intraindividual standard deviation across test scores (IAV Cognitive Domains) significantly predicted probable dementia and this effect was attenuated by interindividual differences in verbal episodic memory. Slope increases in IAV Cognitive Domains across measurement occasions (IAV Time) explained additional risk for MCI and MCI or probable dementia, beyond that accounted for by interindividual differences in multiple cognitive measures, but risk for probable dementia was attenuated by mean decreases in verbal episodic memory slope. These findings demonstrate that within-person variability across cognitive domains both at baseline and longitudinally independently accounts for risk of cognitive impairment and dementia in support of the predictive utility of within-person variability. 1. Introduction There is continued interest in identifying optimal and novel cognitive predictors of dementia of Alzheimer’s type (AD) as both diagnostic and predictive entities [1–5]. Although it may be difficult to discriminate AD in its early preclinical stages from normal cognitive aging, it is believed that preclinical markers of AD may be present in older adults for many years before the appearance of clinical symptoms [6, 7]. While neuropsychological tests of both memory and executive function (EF) have been used to discriminate normal cognitive aging from both mild cognitive impairment (MCI) and AD [8, 9], the role of intraindividual variability among cognitive domains is not well understood. The preclinical onset of dementia is marked by decreases in both overall global and domain-specific cognition [2, 10–13], in particular episodic memory and executive function (EF). Decrements in verbal episodic memory are generally identified as one of the earliest markers of cognitive decline [14–16], followed by global changes in multiple
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