As shown in , patients with mean item SCL scores greater than 2.0 were significantly younger (t226= 2.46, P = .02), had higher neuroticism scores (t225= 2.09, P = .04), had the onset of their first depressive episode at an earlier age (t226= 3.47, P < .001), and were significantly more likely to have comorbid panic disorder (χ21= 13.79, P < .001) compared with patients with SCL scores from 1.0 to 2.0. As would be expected, patients in the two SCL strata had significantly different baseline SCL scores (t226= 19.31, P < .001). The SCL severity groups did not differ in gender, education, employment, race, chronic disease score, or percent of patients with recurrent depression or dysthymia.
Demographic and Clinical Characteristics of Patients in the Depression Strata
Patients with SCL scores greater than 2.0 rated themselves as having significantly more stress over the past 3 months (t225= 2.44, P = .02) and stated that the stress interfered with their daily activities more than patients with less-depressive severity (t226= 2.86, P = .004)(). They also rated themselves as significantly more lonely (t226= 4.03, P < .001) and as having more childhood emotional abuse (t226= 4.02, P < .001). The groups did not differ on any other social support or vulnerability variables. There were no differences between the groups with respect to the percentage of patients seeing a mental health provider, number of primary care visits for depression, number of visits for other medical problems, or number of visits or telephone calls related to the intervention over the 6-month time period.
To summarize the univariate findings, age, neuroticism, stress level and interference from stress, comorbid panic disorder, age of onset of first depression, loneliness, and childhood emotional abuse were allowed to enter in a stepwise fashion into a logistic regression model predicting SCL depression group severity strata. Both backwards and forwards methods were employed. Both techniques produced the same model with three significant independent predictors of SCL severity status: comorbid panic disorder (Wald's t = 11.14, P < .001), loneliness (Wald's t = 9.46, P < .002), and childhood emotional abuse (Wald's t = 5.42, P < .02). Patients in the high severity SCL group were more likely to have comorbid panic disorder (odds ratio [OR], 5.8), to feel more lonely (OR, 2.6), and to have experienced childhood emotional abuse at least “sometimes” (OR, 2.1), compared with patients in the lower SCL group.
As seen in , intervention patients in the lower SCL severity group were significantly more likely to improve over time compared with usual care patients (z = −3.06, P < .002). Conversely. shows that in the more severely ill depression group, there was no significant group-by-time effect (z = 0.61, P = NS), although both intervention and usual care groups had a significant decrease in depressive symptoms over time (z = −7.09, P < .001). Interestingly, in the more severe group, collaborative care appears to produce a more significant change in first 3 months (similar to the differences found between the less severe intervention vs control groups), yet that difference disappears between 3 and 6 months.
SCL depression adjusted means (adjusted for age, gender, chronic disease score, and neuroticism) with standard errors for patients in the high severity strata.
SCL depression adjusted means (adjusted for age, gender, chronic disease score, and neuroticism) with standard errors for patients in the low severity strata.
presents the percentages of adequacy of antidepressant dose, adherence to medications, and the percentage of patients taking selective serotonin reuptake inhibitors (SSRIs) in the care as usual and the intervention groups classified by depression severity. Adequacy is shown in both the lowest dose, consistent with ACHPR guidelines, and twice the lowest dose. Intervention patients in both severity groups received more intensive pharmacotherapy and were significantly more likely to receive an adequate dose of antidepressants for 90 days or more compared with usual care controls. Despite the lack of significant effects on depressive symptoms between intervention and usual care patients in the high severity group, self-report data show that the intervention patients in the high severity group were significantly more likely to have taken medication for 25 or more days during the prior month at the 6-month follow-up. Compared with the usual care patients, the intervention patients in the high severity group were also more likely to be taking SSRIs at the 6-month follow-up.
Adequacy and Adherence Percentages for Intervention and Control Groups Within the Low and High Depression Strata
To investigate whether differences in antidepressant adherence between intervention and usual care patients might explain the disappearance of treatment response in the high depression severity intervention group , we examined automated data on refills during this period. We compared intervention and controls in the high severity group with respect to gaps of 15 days or more in their antidepressant adherence for the interval between 3 months (the end of the intervention) and 6 months. We found that, compared with usual care patients, significantly fewer intervention patients in the high depression severity group had refill gaps of 15 days or more (38.7% vs 61.3%). This suggests that the intervention patients had a more continuous adherence to medications than controls between 3 and 6 months, despite having increased depression symptoms.