The sources of convergence between measures of apathy and depression.

Apathy and depression are discriminable but related dimensions of behavior. The purpose of this study was to evaluate the source of the overlap between measures of apathy and depression. We evaluated the intercorrelations between the Apathy Evaluation Scale (AES) and the Hamilton Rating Scale for Depression (HamD) in 107 subjects, aged 53-85, who met research criteria for normal aging, left or right cerebral hemisphere stroke, probable Alzheimer's disease, or major depression. We determined the correlation between the individual items on the HamD and the total scores on the AES and the HamD. The HamD items having the strongest correlations with AES total score were diminished work/interest, psychomotor retardation, anergy, and lack of insight. The correlation between AES and HamD total scores was nonsignificant when major depression subjects and these variables most closely related to apathy were excluded from consideration. These findings indicate that the convergence between HamD and AES is attributable to (i) a subset of HamD items which are consistent with the syndrome of apathy and (ii) the fact that major depression is associated with both apathy and depression. Clinical and research applications of these results are discussed.