Are there meaningful differences between major depressive disorder, dysthymic disorder, and their subthreshold variants?

A number of researchers have proposed adding an increasing number of subthreshold variants of major depressive disorder (MDD) as new mood disorder. However, this research has suffered from a number of theoretical and methodological flaws that the current investigation has attempted to address. Individuals with MDD (n = 470) were compared with individuals with subthreshold MDD (n = 57). Individuals with MDD reported consistently more severe symptoms, albeit of small magnitude, as well as differences in comorbidity with only two disorders. Results also indicated that diagnosis did not significantly predict rate of symptom change when MDD was compared with its subthreshold variant. Taken together, the aforementioned evidence suggests that small differences exist between MDD and its subthreshold variant. In addition, the extent to which the latter serves as useful analogs for the former may depend upon the variables under study.