Of 1415 subjects approached for study enrollment, 709 (50.l %) completed intake assessments. As reported elsewhere (23
), while complete information on non-enrolled subjects was not available due to the Health Insurance Portability Accountability Act, enrolled subjects did not differ from non-enrolled patients on age, gender, or 15-item Geriatric Depression Scale (33
) score based on available data. Of 709 enrollees, 499 returned completed NEO-FFI forms. Of these 499, 488 completed the cognitive and depressive measures and were included in this study; the remaining 221 were excluded. To assess sub-sample representativeness, a logistic regression compared subjects with demographic, CIRS, depressive measures and MMSE who completed the NEO-FFI versus those who did not. Only MMSE score (β = 0.16, Wald χ2
= 13.18, df = 1, p = 0.0003) and completion of Trails A and Trails B (β = 1.17, Wald χ2
= 17.13, df = 1, p < 0.0001) were associated with group membership: subjects with completed NEO-FFI had higher MMSE scores (28.2 (±1.6) vs. 27.8 (±1.9)) and subjects who completed the Trails A and Trails B were more likely to have completed the NEO-FFI (OR = 3.23, 95%CI = 1.85, 5.62).
Descriptive data are reported in . Of the 80 subjects with major depression, 23 had current and 57 partially remitted major depression; of 79 with minor depression, 32 had current and 47 a partially remitted disorder. Twenty-nine (37%) of the patients with major depressive disorder had late-onset depression, while 52 (68%) of the patients with minor depression had late-onset depression.
Demographics and Descriptive Data
shows the results of the multivariate analyses where the p-values are reported for the associated χ2
tests subsequent to the estimating equations analysis. Multi-collinearity was not detected in any of the models since the VIF for all models were less than 3, much smaller than the recommended threshold of 10 (32
). Testing the first hypothesis in the overall sample, neuroticism was significantly associated with MMSE score, but not with the measures representing executive function. Neither depression diagnosis (χ2
= 0.97, df = 2, p = 0.62; represented by two vectors, one which compared the major depression disorder group and non-depressed group and the second which compared the minor depression disorder group with the non-depressed group) nor depressive symptoms were associated with MMSE scores. Also, depression was not associated with the other cognitive measures in the overall sample.
Predictors of Cognition: Neuroticism and Depression
Turning to the analyses to test the second hypothesis of the moderating effects of depression (not shown in ) the neuroticism by depression diagnosis interaction term suggests an association with MMSE scores, using a more conventional p < 0.05, although it was not statistically significant by the more conservative p < 0.01 (χ2 = 7.21, df = 2, p = 0.03). The major component contributing to the interaction was the minor depression group (β = −0.08, χ2 = 6.94, df = 1, p=0.008, 95%CI = −0.14, −0.02), while for the major depression group (β = −0.03, χ2 = 1.48, df = 1, p = 0.22, 95%CI = −0.09, 0.02) and the non-depressed group (β = −0.02, χ2 = 2.08, df = 1, p = 0.15, 95%CI = −0.05, 0.01) interactions did not achieve significance. For participants who scored one standard deviation above the mean NEO-FFI score for neuroticism, MMSE scores dropped by 0.23 in those with major depression and by 0.62 in those with minor depression. The neuroticism by depression diagnosis interaction term was not associated with executive function. The neuroticism by Ham-D interaction term was not associated with MMSE score (β = −0.001, χ2 = 0.55, df = 1, p = 0.46, 95% CI = −0.004, 0.002) or any of the cognitive measures.
In the sensitivity analyses that compared subjects with major depression versus nondepressed (excluding minor depression, not shown in ), neuroticism’s association with MMSE was strongly suggestive independent of depression diagnosis (β = −0.03, χ2 =5.13, df = 1, p = 0.02, 95% CI = −0.06, −0.004) but not independent of Ham-D scores (β = −0.02, χ2 = 3.24, df = 1, p = 0.07, 95% CI = −0.05, 0.002). Depression diagnosis, although not significant, had a suggestive association with scores on both Trails A (β = 7.27, χ2 = 4.07, df = 1, p = 0.04, 95% CI = 0.19, 14.36) and Trails B (β = 16.17, χ2 = 4.29, df = 1, p = 0.04, 95% CI = 0.83, 31.52). The neuroticism by depression diagnosis and neuroticism by Ham-D scores interaction terms were not associated with any of the cognitive measures.
In the sensitivity analyses focusing on the effects of late-onset depression (not shown in ), an association between neuroticism and MMSE score (β = −0.03, χ2 = 5.37, df = 1, p = 0.02, 95% CI = −0.06, −0.005) was observed independent of depression diagnosis, but the neuroticism by depression diagnosis interaction term was not statistically significant. The interaction of neuroticism by depression diagnosis group was suggestive (χ2 = 6.60, df = 2, p = 0.04) for Trails A (β = 0.66, χ2 = 1.47, df = 1, p = 0.23, 95% CI = −0.41, 1.73 for the major depression group, β = −0.96, χ2 = 4.40, df = 1, p = 0.04, 95% CI = −1.85, −0.06 for the minor depression group, β = 0.28, χ2 = 2.06, df = 1, p = 0.15, 95% CI = −0.10, 0.65 for the non-depressed group) but not significant for Trails B or the Mattis-IP. When controlling for Ham-D scores, neither neuroticism nor the neuroticism by Ham-D interaction term were statistically significant for performance on MMSE in those with late-onset depression vs. those who were nondepressed. Ham-D scores’ association with Trails A scores was suggestive (β = 0.48, χ2 = 3.89, df = 1, p = 0.05, 95% CI = 0.002, 0.97), but not with other cognitive measures. None of the neuroticism by Ham-D interaction terms were associated with Mattis-IP or Trails A or B scores.
In the sensitivity analyses that compared subjects with current major and minor depression versus nondepressed (excluding partially-remitted major or minor depression, not shown in ), neuroticism’s association with MMSE was strongly suggestive independent of depression diagnosis (β = −0.03, χ2 =4.83, df = 1, p = 0.03, 95% CI = −0.06, −0.003) but not independent of Ham-D scores. The neuroticism by depression diagnosis and neuroticism by Ham-D scores interaction terms were not associated with any of the cognitive measures.