Purpose: Both major depressive disorders (MDD) and subthreshold depressions (SD) are more prevalent among subpopulations of elders with functional disability. This study addresses (1) what symptoms are common and unique to SD and MDD, and (2) what associative factors are common and unique to SD and MDD.

Method: Our sample derived from the first wave of a longitudinal study of depression among clients age 60 and above entering public community long term care in the state of Missouri from August 2000 to January 2005 (307 non-depressed, 213 SD, and 75 MDD). We used the computerized, screening version of the Diagnostic Interview Schedule to establish diagnoses of MDD, and SD was identified by the modified twenty CES-D items with a score greater than 9 among elders who did not meet MDD criteria.

Results: First, chi-square tests failed to find any difference of frequency of CES-D items between the two groups. For example, 89.3% of MDD reported they felt depressed and 90.1% of SD did (chi-square=0.04, df=1, p=.85). Second, t-tests indicated no mean difference of CES-D scores between the two groups (t=0.34, df=95.5, p=.73; mean of MDD=11.40, mean of SD=11.55). To compare correlates between SD and MDD, multinominal logistic regression was run for the whole sample. Results of multinominal logistic regression analysis for a three-level dependent variable (reference group: non-depressed) indicated that common associative factors of SD and MDD include lower education, greater functional limitations and chronic conditions, poorer social support, and higher stress. Unique associative factors of MD include being younger, not married, and greater negative life events. In contrast, a unique associative factor of SD is having difficulties of affording food.

Implications: First, our findings lend support to the continuum notion of depression; that is, the idea that the symptoms and characteristics between subthreshold depression and major depressive disorders may differ in degree along a continuum. Identification of only older adults who meet criteria for major depressive disorder would leave many elders with substantial depressive symptoms undiagnosed and untreated. Second, our findings confirm the significant role of stress, comorbidity, and social isolation in later-life depression. Findings may inform the identification of older adults suffering major depression and significant depression symptomatology in systems of community care. Finally, reimbursement issues need to be resolved for elders with SD to receive appropriate interventions as reimbursement requires diagnosis of major depression.