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 elderly. Sensory disability, grip strength, and speed of processing have been established as associates of cognitive performance in cross-sectional studies. However, it is not known whether changes in these predictor variables are associated with changes in cognitive functioning. OBJECTIVES: (1) to examine the relationship between initial level of three predictor variables - speed of processing, sensory disability, and grip strength - and changes in memory and crystallized intelligence (CIQ); (2) to examine the relationships between change in grip strength, cognitive speed, and sensory disability and changes in memory and CIQ, and (3) to investigate these relationships with the effects of age and sex statistically removed. METHODS: Cognitive ability was assessed in two domains: CIQ (3 tests) and memory (3 tests) measured on two occasions approximately three and a half years apart in a large community sample (n = 425; mean age = 75.8, range 70-93 years). Repeated-measures Anova was used to analyze descriptive data. Latent-change models were used to examine structural relationships between constructs. RESULTS: Initial levels of reaction time or grip strength did not predict rate of change on memory tasks. Changes in grip strength, speed, and memory correlated moderately, suggesting that these variables have some tendency to move together over time. Sensory disability correlated with age but not with change in speed, grip, memory, or CIQ. These relationships held across the age range 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 our analysis. Cross-sectional and longitudinal data sets yield different interpretations about the basic component associates of cognitive performance.