Demographic and clinical characteristics of the sample are described in .
Baseline characteristics of all participants across categories based on depression trajectories over time
At baseline (MoVIES Wave 2), the cohort included 1341 members, 1260 of whom were included in the current analyses after excluding 48 participants with dementia onset prior to the baseline assessment, 21 participants with incomplete mCES-D data at baseline, and 12 participants with incomplete MMSE data.
Overall follow-up of this cohort extended up to 11.8 years after baseline (Wave 2) assessment, with a median of 8.3 years. During this period, 41.7% (n=526) participants died, and 8.5% (n=107) were lost from the cohort for other reasons (dropout, too ill, or relocation). The trajectory analyses included all participants assessed at baseline regardless of how long they were followed subsequently. The mean (SD) interval between consecutive waves was 2.4 (0.3) years. Pearson correlation coefficients between total mCES-D scores were strongest for adjacent waves and became weaker for waves further apart.
Depressive symptoms profiles
In the factor analysis of the mCES-D, a four-factor solution was retained according to the Kaiser criterion (eigenvalues > 1). These four factors cumulatively accounted for 55% of the variance of the original matrix. All items included in the four respective factors achieved loading ≥ 0.45. Two items – restless sleep and feeling fearful – failed to load at the specified level. Four factors of mCES-D items based on this factor structure were used to characterize participants’ symptom profiles.
Profile 1 was based on the first factor which accounted for 28% of the variance of the original matrix. These symptoms included feeling depressed, not feeling happy, feeling lonely, feeling sad, not being able to shake off the blues, crying. We designated this profile as Core Mood Symptoms.
Profile 2 was based on the second factor which accounted for 9% of the variance. It included thoughts that others were unfriendly, that others disliked her/him, that life had been a failure. We refer to this profile as Self- Esteem/Interpersonal Symptoms.
Profile 3 was based on the third factor which accounted for 12% of the variance. It included poor appetite, not feeling hopeful, not enjoying life, feeling that one could not get going, feeling everything was an effort, not enjoying life, not feeling just as good as other people. We refer to this profile as Anhedonia/Neurovegetative Symptoms.
Profile 4 was derived from the fourth factor which accounted for 6% of the variance. It included a heterogeneous group of symptoms reflecting concentration (trouble keeping mind on what she/he is doing), withdrawal (talked less than usual) and increased sensitivity (being bothered). We refer to this profile as Mixed Symptoms.
We note that profiles 1 to 3 above – core mood, anhedonia/vegetative symptoms, and self-esteem/interpersonal difficulties – derived from the mCESD, are consistent with those described recently by Shafer (2006)
in a metaanalysis of factor analyses of the original CES-D (Radloff, 1977
Trajectories of depressive symptoms
Trajectory analysis revealed six trajectories of total mCES-D scores over time; trajectories 1 through 3 had linear forms while trajectories 4 through 6 were quadratic (see ); the BIC showed no improvement in model fit beyond the six-trajectory model. In examining characteristics of the entire sample and of each trajectory group, global tests showed that all selected variables were significantly different among the six trajectory groups (see ). Trajectory groups 1 and 2 (TG1 and TG2), which together included the largest number of participants, reported one or no depressive symptoms at baseline with virtually no change in symptom score during follow-up. They were therefore not included in further comparisons.
Trajectory group 3 vs. trajectory group 4
Trajectory groups 3 and 4 (TG3 and TG4) were selected for the first pairwise comparison because both reported sub-threshold (<5) depressive symptoms at baseline, but TG3 subsequently had a flat trajectory over follow-up while TG4 showed an increase in symptom score over time (see ). We characterize TG3 as the “stable low-depressed” group and TG4 as the “emerging depressive symptoms” group. In univariable analyses (), compared to TG3, those with emerging depressive symptoms (TG4) were significantly more likely to be women, with lower levels of education, marginally lower cognitive status, at least one impaired IADL, and to report taking a higher number of prescription drugs at baseline. Although a larger proportion of the TG4 than the TG3 participants died during follow-up, this difference was not statistically significant (see ).
Stable low-depressed trajectory group (TG3) versus emerging depression trajectory group (TG4): baseline characteristics
In the multivariable analysis comparing TG3 and TG4, only being female and having at least one IADL impairment at baseline were independently associated with future emerging depression. None of the baseline symptom profiles distinguished between groups TG3 and TG4 (see ).
Trajectory group 5 vs. trajectory group 6
Trajectory groups 5 and 6 (TG5 and TG6) were selected for the second pairwise comparison because they both had relatively high mean total mCESD baseline scores. Both trajectories showed a decrease in symptom count over time but their slopes were different (−1.7 vs. 0.1, p < 0.001; see ). TG5 will be described as the “remitting depressive symptoms” group and TG6 as the “persisting depressive symptoms” group. In univariable analyses, TG6 participants were significantly older than TG5 participants, but the groups were similar on other demographic variables (). Also, participants in TG6 had significantly higher baseline mCES-D scores, took significantly more prescription drugs overall, and a higher proportion took antidepressant drugs (see ). With regard to baseline symptom profiles, when compared with TG5, TG6 had higher scores on interpersonal/self esteem and on the anhedonia/neurovegetative profiles. A significantly higher proportion of TG6 than TG5 participants died during follow-up (see ).
Remitting depressive symptoms group (TG5) versus persisting depressive symptoms group (TG6): baseline characteristics
In the multivariable analyses comparing TG5 and TG6, variables independently associated with the persisting depressive symptoms trajectory were: taking more prescription drugs, having higher scores on the interpersonal/self-esteem difficulties and anhedonia/neurovegetative profiles (see ).
Variables excluded from multivariable models
Two baseline characteristics significant in the univariable analyses were excluded from the multiple regression models. By definition, higher baseline total mCESD scores described the higher trajectories; they were also collinear with the symptom factor scores. Total scores were therefore excluded. Antidepressant use at baseline was excluded from both models because of the very small number of individuals reporting this variable in all trajectory groups (); although the association between TG6 and antidepressant use was statistically significant, the estimates were unstable with very wide confidence intervals.
Some covariates significant in the univariable analyses were no longer significant in the multiple regression models. To determine whether the loss of significance was due to loss of power after adjusting for covariates, power calculations were performed using PASS 2005 (Hintze, 2005
). For the regression model comparing TG3 and TG4, we had 80% power at the 0.05 significance level for all covariates except the MMSE. For the regression model comparing TG5 and TG6, we had 80% power at the 0.05 significance level for all covariates except age and IADL.
A Cox proportional hazards model was fitted to predict mortality in the cohort as a function of depressive symptom trajectory. Using TG1 as the reference group, all five higher trajectories (TG2 through TG6) were significantly associated with time to death, after adjusting for age, sex and number of prescription medications (reflecting medical burden). The hazard ratios (with 95% confidence intervals) for TG2 through TG6 were 3.5 (1.9–6.5), 4.1 (2.2–7.6), 4.3 (2.1–8.5), 2.9 (1.3–6.4), and 9.6 (4.4–21.0).