The occurrence of life-change events (as defined by the social readjustment rating questionnaire) prior to disease onset was measured in a group of 74 patients suffering from primary depressive disorders. The resultant frequency distribution histogram was unimodal. Patients with a positive family history for depression did not differ significantly, in these measurements, from those with a negative family history nor did patients with "endogenous" depression differ significantly from those with "reactive" depression. We were, therefore, unable to distinguish two populations within the depressed group using this parameter. We conclude that the terms "endogenous" and "reactive" are misleading for the majority of patients with depressive illness.
Thomson KC, Hendrie HC. Environmental Stress in Primary Depressive Illness. Arch Gen Psychiatry. 1972;26(2):130-132. doi:10.1001/archpsyc.1972.01750200034007