At baseline, 44% of our highly selected cohort fulfilled NIMH-dAD criteria for depression. Demographic comparisons between depressed and nondepressed individuals () indicated that those who were depressed were marginally more likely to be female and had marginally fewer years of formal education. There were no significant differences between the depressed and nondepressed groups in age or MMSE scores. Four participants (three depressed, one nondepressed) were excluded from the MMSE analysis due to miscoded data for one or more individual items. Demographic differences between the depressed and nondepressed groups did not survive Bonferroni correction (critical p = 0.0125).
Baseline Demographic Data for Depressed and Nondepressed Participants as Diagnosed With the NIMH-dAD Criteria
Baseline rates of depression varied across assessment tools (; χ2 = 55.46, df = 5,100, p <0.001). Unadjusted comparisons indicated that the use of NIMH-dAD criteria resulted in higher rates of depression than the criteria for DSM-IV major depression (14%; Z = −5.5, df = 101, p <0.001) or DSM-IV criteria for major or minor depression (36%; Z = −2.31, df = 101, p = 0.021). The NIMH-dAD criteria also identified more patients as depressed than established cut-offs for the CSDD (30%; Z = −2.86, df = 101, p = 0.004) and the GDS (33%; Z = −2.04, df = 101, p = 0.041), but not the NPI-Q (50%; Z = −1.22, df = 100, p = 0.22). One participant, who did not meet NIMH-dAD criteria for depression, was missing baseline data for the NPI-Q dysphoria item and therefore was excluded from analyses involving this item. After Bonferroni correction (critical p = 0.01), NIMH-dAD criteria continued to produce significantly higher rates of depression than the criteria for DSM-IV major depression and the CSDD. Demographic comparisons between depressed patients identified with each assessment tool indicated that there were no significant differences in age, gender, education, antidepressant medication use, or MMSE scores between individuals identified with NIMH-dAD criteria versus the other assessments.
Baseline Rates of Depression as Determined With Different Assessment Tools
Investigation of the concordance between the different assessment tools indicated that diagnoses obtained with NIMH-dAD criteria most closely reflected those obtained with DSM-IV criteria for major or minor depression (). Relative to DSM-IV criteria for major depression, NIMH-dAD criteria exhibited sensitivity of 100%, specificity of 66%, positive predictive value (PPV) of 34%, and negative predictive value (NPV) of 100%. Relative to DSM-IV criteria for major or minor depression, NIMH-dAD criteria exhibited sensitivity of 94%, specificity of 85%, PPV of 77%, and NPV of 96%.
Concordance of Baseline Diagnoses With the NIMH-dAD Criteria With Diagnoses Obtained Using the Other Assessment Tools
Analyses of the frequencies of the individual symptoms specified by NIMH-dAD criteria indicated that, as expected, depressed mood and decreased positive affect / pleasure were the most commonly reported symptoms among the depressed participants, since at least one of these two symptoms is required for a diagnosis of depression (). Conversely, appetitive disturbances and suicidality were the least commonly reported symptoms. Depressed individuals exhibited significantly more NIMH-dAD symptoms than nondepressed individuals (5.23 versus 1.04; t = 13.96, df = 99, p <0.001). Separate chi-square tests with Bonferroni correction (critical p = 0.005) indicated that all NIMH-dAD symptoms except for irritability (χ2 = 4.85, df = 1,101, p = 0.028) and suicidality (χ2 = 7.35, df = 1,101, p = 0.007) were significantly more common among depressed than nondepressed participants. Multivariate logistic regression analysis of the association between individual NIMH-dAD symptoms (excluding the two obligatory symptoms) and a diagnosis of depression yielded a Nagelkerke R2 of 0.71 and indicated that only psychomotor changes (β = 2.05, SE: 0.82; Wald χ2 = 6.27, odds ratio [OR] = 7.8, 95% confidence interval [CI]: 1.6–38.8; p = 0.012), fatigue (β = 2.83, SE: 0.82; Wald χ2 = 11.89, OR = 16.9, 95% CI: 3.4–84.2; p=0.001), and a sense of guilt / worthlessness (β = 3.46, SE: 1.05; Wald χ2 = 11.80, OR = 32.0, 95% CI: 4.1–252.4; p = 0.001) were independently predictive of depression. The model was not adjusted for baseline demographic variables or MMSE scores given the absence of significant differences between the depressed and nondepressed groups on these measures.
Baseline Frequencies of Individual NIMH-dAD Symptoms in Depressed and Nondepressed Participants
Ninety participants (89%) returned for follow-up assessment after a 3-month interval. Participants who were lost to follow-up had significantly fewer years of formal education (11.9 versus 14.3; t = 2.19, df = 99, p = 0.031) and marginally lower MMSE scores (18.4 versus 21.4; t = 1.76, df = 95, p = 0.081). At baseline, they were more likely to be diagnosed with depression using the criteria for DSM-IV major depression (36% versus 11%; χ2 = 5.26, df = 1,101, p = 0.022) or the NPI-Q (82% versus 47%; χ2 = 4.70, df = 1,100, p = 0.03) or to be receiving treatment with antidepressant medications (64% versus 31%; χ2 = 4.58, df = 1,101, p = 0.032) than participants that returned for follow-up. Remission rates at 3 months for depression diagnosed at baseline with the different assessments ranged from 32% to 61% (). There were no significant differences in remission rates between assessment tools (χ2 = 5.59, df = 6,170, p = 0.35). Five participants were missing data from at least one assessment tool at follow-up and were excluded from this analysis.
Remission Rates for Depression at 3 Months Among Participants Diagnosed With Depression at Baseline With Different Assessment Tools