The relationship between short-term intraindividual variability and longitudinal intraindividual cognitive change in older adulthood: covariation and prediction of change




Bielak, Allison Anne Marie

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This dissertation presents two studies of intraindividual variability in a longitudinal context to further explore the relationship between short-term intraindividual variability and longer-term cognitive change in older adults. A sample of 304 community-dwelling older adults initially aged 64-92 years completed between 1 to 6 waves of annual testing over a 5-year period. Participants completed an extensive battery of accuracy- and latency-based tests covering a wide range of cognitive complexity. The first study addressed the longitudinal nature of intraindividual variability over 3 years. Group-based increases in inconsistency were limited to the latter half of older adulthood (i.e., 75 years and older), but there were significant individual differences across the entire sample. The covariation relationships between change in cognition and change in inconsistency were significant across the one-year interval, and found to remain stable across both time and older age. For each additional unit increase in intraindividual variability, participants’ cognitive performance correspondingly declined. The strength of the coupling relationship however was stronger for fluid cognitive domains such as memory, reasoning, and processing speed, and variability based on moderately and highly complex tasks provided the strongest prediction. Building on these results suggesting that intraindividual variability is highly sensitive to even subtle changes in cognitive ability, the second study addressed the capacity of intraindividual variability to predict cognitive ability and other meaningful change outcomes 5 years later. Inconsistency at Wave 1 was particularly sensitive to changes reflecting the early behavioural characteristics of dementia, including episodic memory ability, cognitive status, and attrition. In each case, greater inconsistency at baseline was associated with a greater likelihood of being in a maladaptive group 5 years later. Mean rate of responding was a comparable predictor of change in most instances, but differences emerged according to the complexity of their derived tasks. Variability based on moderate to high cognitively challenging tasks appeared to be the most sensitive to longitudinal changes in cognitive ability, and was uniquely predictive of the rate of attrition compared to neuropsychological tasks. These findings are promising of the potential utility and applicability of intraindividual variability in understanding and predicting intraindividual cognitive change in older adulthood.



Development, Lifespan, Cognition, Aging