Comorbidity of unipolar depression: I. Major depression with dysthymia.

The degree of current and lifetime comorbidity between major depressive disorder (MDD) and dysthymia (DY) was examined in large community samples of older adolescents (n = 1,710) and adults (n = 2,060). DY was highly comorbid with MDD (lifetime odds ratio of 3.4 for adolescents and 1.6 for adults) and was more likely to precede than to follow MDD, especially in persons who became depressed early in life. MDD was by far the more frequent form of depression: Approximately 80% of the depressed persons experienced only MDD, 10% experienced only DY, and 10% experienced both MDD and DY. The large number of persons who had became depressed twice experienced MDD in the 2nd episode, regardless of the nature of the 1st depression. History of depression was associated with a greater probability for other mental disorders in both adolescents and adults; however, the rates of comorbidity for MDD did not differ from rates for DY or for both MDD and DY.