Of 750 subjects completing the study intake, 17 had died and 484 (64.5% of the initial group) remained in the study at one-year follow-up. (Note that while all 484 provided one-year Ham-D scores, 482 had one-year SCID depression diagnosis data.) Of those completing one-year follow-up, 299 (61.8%) were female and 455 (94.0%) were white. Four hundred and thirty (88.8%) had been recruited from general internal medicine practices, 26 (5.4%) from geriatric primary care, and 28 (5.8%) from family medicine practices. Other descriptive data at intake for those completing one-year follow-up are provided in . Compared with those not completing follow-ups, those included in the present analyses did not differ significantly in age, gender, education, depression diagnosis, Ham-D score, or CIRS score, but were more likely to be white (OR [95% CI] 2.5 [1.4–4.5], χ2 = 8.8, df = 1, P = 0.003). Baseline NEO personality forms were received from 368 subjects (76.0% of those completing one-year follow-ups); NEO completers were more likely to be white (OR [95% CI] 3.0 [1.2–7.3], χ2 = 5.6, df = 1, P = 0.018) but did not differ in age, gender, education, depression diagnosis, Ham-D, or CIRS scores.
Descriptive data by depression diagnosis group at study intake. Values are shown as N, mean (SD), range unless otherwise specified
Depression outcomes by initial depression diagnosis
shows a bivariate cross-tabulation of depression diagnoses at study intake and one-year. Multivariate proportional odds models controlling for age, gender, education, and CIRS score revealed that baseline depression diagnosis as a whole was a significant predictor of follow-up diagnosis (χ2 = 99.9, df = 2, P < 0.001). At follow-up the Min/SSD group was more likely than the non-depressed group to meet diagnostic criteria for Min/SSD or major depression (χ2 = 77.5, df = 1, P < 0.001), although their outcomes were better than the group with major depression at baseline (χ2 = 13.0, df = 1, P < 0.001). Controlling for baseline age, gender, education, and CIRS score, patients in the Min/SSD group were 7 times more likely (95% CI 4.5–10.8; χ2 = 77.4, df = 1, P < 0.001) than the non-depressed group to develop major depression, while patients in the major depression group were 50.3 (95% CI 16.6–152.1; χ2 = 48.0, df = 1, P < 0.001) times more likely than the non-depressed group to have major depression one year later. However, the proportion of Min/SSD subjects developing major depression was fairly low, and many improved to the non-depressed group at one year. Secondary analyses examining differences between minor and SSD subgroups showed that the minor depression subgroup was 12.6 times more likely (95% CI 5.5–29.1; χ2 = 60.5, df = 1, P < 0.001) than the non-depressed group to move into major depression at one year, while the SSD subgroup was 6.1 times more likely (95% CI 3.9–9.6; χ2 = 35.2, df = 1, P < 0.001) than the non-depressed group to move into major depression at one year; a statistically non-significant difference between the two levels of depression (χ2 = 2.8, df = 1, P = 0.10).
Depression diagnosis at intake and one-year follow-up
Similarly, as shown in , the baseline non-depressed, Min/SSD and major depression groups also showed a pattern of graded severity with respect to one-year Ham-D scores, adjusted for baseline age, gender, education and CIRS score. Secondary analyses, not shown in the figure, revealed no statistically significant differences in adjusted one-year Ham-D scores between the SSD and Minor Depression subgroups (adjusted one-year Ham-D scores (SE) 12.3 (0.9) vs. 10.6 (0.5), P = 0.09).
Figure 1 Adjusted one-year Hamilton Depression Rating Scale scores by baseline depression diagnosis. One-year scores adjusting for age, gender, baseline Cumulative Illness Rating Scale score pair-wise comparisons: Minor/subsyndromal depression vs. non-depressed (more ...)
Predictors of depression outcomes
The final multivariate models for all predictors (for the entire sample, thus excluding personality) are shown in . The significant independent predictors of depression diagnosis at one year were white race and baseline depression diagnosis, GAF score, social interaction, and perceived social support. Results were unchanged when minor depression and SSD were treated as separate subgroups. The independent predictors of one-year Ham-D score were baseline scores on the Ham-D, physical functioning (KPSS), psychiatric functioning (GAF), perceived social support, and instrumental social support. In all final models, the direction of the effect was such that higher baseline symptoms and poorer functioning or social support predicted poorer depressive outcome.
Final multivariate models predicting depression outcome
The addition of the NEO-FFI personality traits to the prediction models yielded largely similar findings, with differences from the above-described models mainly attributable to sample restriction among those who completed and returned the NEO-FFI questionnaires. In the sensitivity analysis that simultaneously entered all variables significant at P < 0.20 in bivariate comparisons, neuroticism was marginally significant in its association with one-year depression diagnosis (for each +1 SD in neuroticism, OR (95% CI) 1.5 (1.0–2.2); χ2 = 3.8, df = 1, P = 0.05).