The mean age and education ± standard deviation of the sample were 81.1 ± 5.8 and 12.5 ± 3.1 years, respectively; 70% were women; 98.1% were white; and 41.5% lived alone. The distribution of IQCODE scores was skewed to the right and had the following characteristics: range, 2.63 to 5.00; median, 3.13; and mean, 3.30 ± 0.51.
Twenty-three subjects (14.4% of the sample) met the criteria for cognitive decline, representing an incidence density of 48.6 cases per 1,000 person-years at risk. presents descriptive statistics for the sample and the bivariate relationships between the study measures and dementia status at follow-up. The relationships are reported as incidence density ratios, which are based on Poisson regressions with number of years from the 1-year assessment to follow-up as an offset variable. shows that age, sex, education, change in visual acuity, and number of dropped activities were associated with dementia at follow-up; each 5-year increment in age increased dementia risk by 57%; each 4-year increment of education increased the risk by 36%; and each additional dropped activity increased the risk by 57%. Thus, subjects who relinquished three activities, for example, were 3.87 times (95% confidence interval [CI], 1.95 to 7.76) more likely to become demented than subjects who relinquished no activities. The risk for subjects who relinquished five activities increased to 9.54 times (95% CI, 3.05 to 30.43).
Bivariate IDRs of study measures with dementia status at follow-up (n = 160)
Baseline abbreviated MMSE score, visual acuity in the better eye, medical comorbidity (ie, Chronic Disease Score), vascular risk factors, and treatment assignment (PST vs usual care) were unrelated to dementia risk. During the 1-year clinical trial, decline by more than one point on the abbreviated MMSE, incident depressive disorder, and changes in medical comorbidity were also unrelated to dementia risk. There was no significant correlation between number of dropped activities and baseline abbreviated MMSE (r = 0.05, P = .525) or change in MMSE scores from baseline to 12 months (r = 0.10, P = .213).
shows the results of a multivariate model that included age, number of dropped activities, and their interaction. Although education, sex, and change in visual acuity were significant at the bivariate level, when added to the model they did not meet the criteria for confounding and were thus not included in the final model. The interaction term of age × dropped activities was significant (P = .013), indicating effect modification by age. For those older than age 80, each additional dropped activity increased the risk of cognitive decline by 27% (IDR, 1.27; 95% CI, 0.99 to 1.63; P = .065). For those younger than 80, the effect was stronger; each additional activity dropped increased the risk of cognitive decline by nearly 200% (IDR, 2.96; 95% CI, 1.59 to 5.52; P ≤ .001).
Poisson generalized estimating equations model predicting cognitive decline