Specificity of the Calgary Depression Scale for schizophrenics

This study sought to determine the specificity of the Calgary Depression Scale (CDS), a depression rating scale for schizophrenics. The specificity is the degree to which the scale assesses depression rather than negative or extrapyramidal symptoms. Subjects were 100 outpatients (OP) and 50 inpatients (IP) meeting DSM-III-R criteria for schizophrenia. Negative symptoms were assessed with the Positive and Negative Syndrome Scale (PANSS); extrapyramidal symptoms were assessed with the Simpson Angus Scale (SA) and depression with the CDS. Results were that the CDS showed no correlation with SA, but weak (0.33) statistically significant correlations with the PANSS negative symptom score in inpatients but not outpatients. Confirmatory factor analysis using Lisrel 6.0 showed that the model hypothesizing specificity of depression, negative symptoms and extrapyramidal symptoms, was significant, with a goodness of fit index of 0.89 and a root mean square residual of 0.07. It is concluded that the CDS achieves a useful degree of separation between measures of depression, negative and extrapyramidal symptoms in subjects with schizophrenia, when combined with the other measures used in this study.