In a study of relationships between alcoholism and unipolar affective disorder, three groups of patients collected in a research clinic were compared: a group with alcoholism without depression, a group with alcoholism plus affective disorder, and a group with unipolar affective disorder alone. The majority of patients with alcoholism and depression had a history of onset of alcoholism prior to that of depression. Patients with alcoholism plus depression more closely resembled those with alcoholism than those with depression. This finding is evidence that it is useful to separate affectively disordered patients into the groups with and without preexisting nonaffective psychiatric illness. The variables that separated alcoholic patients from patients with depression principally involved sociopathic symptoms that began prior to the onset of clinical alcoholism.
Woodruff RA, Guze SB, Clayton PJ, Carr D. Alcoholism and Depression. Arch Gen Psychiatry. 1973;28(1):97–100. doi:10.1001/archpsyc.1973.01750310075011