Are changes in sensory disability, reaction time, and grip strength associated with changes in memory and crystallized intelligence? A longitudinal analysis in an elderly community sample

Background: Little is known about predictors of cognitive changes in the el derly. Sensory disability, grip strength, and speed of processing have been established as associates of cognitive performance in cross-sectional stud ies. However, it is not known whether changes in these predictor variables are associated with changes in cognitive functioning. Objectives: (I)to exa mine the relationship between initial level of three predictor variables sp eed of processing, sensory disability, and grip strength - and changes in m emory and crystallized intelligence (CIQ); (2) to examine the relationships between change in grip strength, cognitive speed, and sensory disability a nd changes in memory and CIO, and (3) to investigate these relationships wi th the effects of age and sex statistically removed. Methods: Cognitive abi lity was assessed in two domains: CIQ (3 tests) and memory (3 tests) measur ed on two occasions approximately ree a nd a ha If yea rs apart in a large community sam pie (n = 425; mean age = 75.8, range 70-93 years). Repeated-m easures Anova was used to analyze descriptive data. Latent-change models we re used to examine structural relationships between constructs. Results: In itial levels of reaction time or grip strength did not predict rate of chan ge on memory tasks. Changes in grip strength, speed, and memory correlated moderately, suggesting that these variables have some tendency to move toge ther over time. Sensory disability correlated with age but not with change in speed, grip, memory, or CIO. These relationships held across the age ran ge studied after adjustment for age and sex. Conclusions: The findings are consistent with the action of a common causal mechanism underlying changes in speed, grip, and memory. A number of methodological caveats arise from o ur analysis. Cross-sectional and longitudinal data sets yield different int erpretations about the basic component associates of cognitive performance. Copyright (C) 2000 S. Karger AG. Basel.