Reliability and validity of a depression rating scale for schizophrenics

The Calgary Depression Scale (CDS) is a nine item structured interview scale, in which each item has a four point measure, each point anchored by descriptors. The scale has been specifically developed to assess depression in schizophrenics. This article describes the testing of the reliability and validity of the CDS. The scale is assessed and compared to three established measures, the Hamilton Depression Rating Scale (HDRS) the Beck Depression Inventory (BDI) and a depression measure derived from the Brief Psychiatric Rating Scale (BPRS). Confirmatory factor analysis demonstrated that the CDS is unidimensional, measuring the same construct in both in- and outpatients. The scale has high internal consistency, significant strong correlations with scores on the Hamilton, Beck and BPRS depression measures, and the presence of a major depressive episode. All items of the CDS significantly discriminate between the presence and absence of a major depressive episode. It is concluded that the CDS is a parsimonious reliable scale which is suitable for assessing depression across both the acute and residual stages of schizophrenia.