The Calgary Depression Rating Scale for schizophrenia in a healthy control group: psychometric properties and reference values.

BACKGROUND: Assessment of depression in schizophrenia is of great importance as depressive signs and symptoms and suicidality are highly prevalent in patients with schizophrenic disorders. The Calgary Depression Rating Scale (CDSS) is the standard assessment instrument for that purpose due to its proven reliability and validity. However, so far no reference values derived from an adequate healthy sample have been published.
METHODS: The present study analyzed CDSS item scores and summary scores in 154 healthy subjects (49% female, mean age 32.8+/-11.7 years) selected from studies as controls for schizophrenic patients.
RESULTS: The total CDSS score was 2.6+/-2.7 (range 0-12), about 1/3 of healthy subjects had scores=0. Gender differences were observed with respect to "early awakening" and "suicidal ideation" with higher scores in females. Total CDSS scores (r=-0.17, P=0.03) and single items were slightly negatively correlated with age. The psychometric properties of the CDSS scale were satisfying (corrected item-score correlations r(tc)=0.33-0.61, internal consistency Cronbach's alpha=0.76, one-dimensional factor structure). CDSS total scores showed a skewed distribution fitting the upper part of a normal distribution. Based on the empirical distribution of CDSS values, reference values were listed for the total group of healthy subjects, and for females and males separately.
CONCLUSIONS: The results corroborate the favourable psychometric properties of the CDSS found previously in clinical samples in a healthy control group. The reference values reported here can assist the clinical use and interpretation of CDSS values and emphasize the usefulness of the CDSS for a thorough assessment of depression and suicidality in schizophrenia.