Abstract
BackgroundOn average, health worsens with age, but many people have periods of improvement. A stochastic model provides an excellent description of how such changes occur. Given that cognition also changes with age, we wondered whether the same model might also describe the accumulation of errors in cognitive test scores in community-dwelling older adults.MethodsIn this prospective cohort study, 8954 older people (aged 65+ at baseline) from the Canadian Study of Health and Aging were followed for 10 years. Cognitive status was defined by the number of errors on the 100-point Modified Min-Mental State Examination. The error count was chosen to parallel the deficit count in the general model of aging, which is based on deficit accumulation. As with the deficit count, a Markov chain transition model was employed, with 4 parameters.ResultsOn average, the chance of making errors increased linearly with the number of errors present at each time interval. Changes in cognitive states were described with high accuracy (R2 = 0.96) by a modified Poisson distribution, using four parameters: the background chance of accumulating additional errors, the chance of incurring more or fewer errors, given the existing number, and the corresponding background and incremental chances of dying.ConclusionThe change in the number of errors in a cognitive test corresponded to a general model that also summarizes age-related changes in deficits. The model accounts for both improvement and deterioration and appears to represent a clinically relevant means of quantifying how various aspects of health status change with age.
Highlights
On average, health worsens with age, but many people have periods of improvement
The cognitive measure The Modified Mini-Mental state Examination [14] is a 100-point scale that was based on Folstein's Mini-Mental State Examination (MMSE) [15]
Analysis Earlier we have shown that the probabilities of transitions between two states n and k (Pnk) can be represented by a modified Poisson distribution [11,12,21]
Summary
Health worsens with age, but many people have periods of improvement. A stochastic model provides an excellent description of how such changes occur. Given that cognition changes with age, we wondered whether the same model might describe the accumulation of errors in cognitive test scores in community-dwelling older adults. Most notice that their cognitive function changes, usually for the worse. Aspects of recent memory are less efficient, especially the divided attention required for working memory [1,2]. How to understand those changes is controversial. We have modeled other age-related changes and demonstrated that a few parameters can be estimated to accurately describe how deficits accumulate with age [11,12]. We investigated how community-dwelling elderly people accumulate errors in cognitive performance over 5–10 years
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