Reliability of the Calgary depression scale for schizophrenia: a meta-analysis

Background: A challenge for clinicians working with individuals diagnosed with schizophrenia is distinguishing depressive symptoms from negative symptoms of schizophrenia. The Calgary Depression Scale for Schizophrenia (CDSS) was developed for this purpose. No review has previously explored its reliability across multiple studies using advanced statistical means.

Objectives: This meta-analysis aimed to quantify the CDSS' internal consistency, inter-rater reliability (IRR) and test-retest reliability.

Method: A systematic literature search was conducted to find articles reporting on the CDSS' reliability. Articles were screened against the inclusion and exclusion criteria, with data extracted from 40 studies. Overall meta-analytic effects were calculated, and for internal consistency and IRR coefficients subsequent analyses explored between-study variation. The small test-retest reliability dataset limited analysis.

Findings: The internal consistency meta-analytic effect was 0.83 (95% CI:0.82–0.84). Higgins I2 indicated an acceptable level of variation between studies' alpha estimates. This suggests all items in the CDSS are measuring the same construct (i.e. symptoms of depression). The IRR meta-analytic effect was 0.88 (95% CI:0.86–0.91), with Higgins I2 indicating high levels of heterogeneity. This was not deemed problematic variance as it is within levels expected for psychometric measures and, therefore, considered acceptable for this literature. This reflects high level of agreement between different raters when using the CDSS on the same client.

Conclusions: This review suggests the CDSS has good internal consistency and excellent IRR. Further research will help understand its test-retest reliability.