Brief reportThe Calgary Depression Rating Scale for schizophrenia in a healthy control group: Psychometric properties and reference values
Introduction
The Calgary Depression Rating Scale (CDSS) (Addington et al., 1990) is recommended to estimate the severity of depression in patients with schizophrenia (Collaborative Working Group on Clinical Trial Evaluations, 1998) and shows superiority compared to the Hamilton Depression Rating Scale (HAMD), the Montgomery-Asberg Depression Rating Scale (MADRS), and other depression scales (Addington et al., 1996, Collins et al., 1996, Reine et al., 1998, El Yazaji et al., 2002).
The superiority of the CDSS originates from its psychometric properties, particularly internal consistency, inter-rater reliability, sensitivity, and specificity (Lancon et al., 1999, Müller et al., 1999, Reine et al., 2000, Sarro et al., 2004). Discriminant and convergent validity have been proven in a large number of studies (e.g. Bernard et al., 1998, Sarro et al., 2004). CDSS total scores show in most settings only low to modest overlap with positive and negative symptoms, and no substantial correlation with extrapyramidal symptoms (Addington et al., 1994, Lancon et al., 1999, Kontaxakis et al., 2000a, Kontaxakis et al., 2000b, Lancon et al., 2000, Müller, 2002, Müller et al., 2002) during acute schizophrenia; in chronic illness states the overlap between positive and depressive symptoms seems somewhat higher (Lancon et al., 2001).
Converging results have shown that cut-off scores of 4–5 points for minor depression and 6–7 points for major depression show diagnostic congruence of the CDSS with conventional classification manuals (DSM-IV) (Bressan et al., 1998, Sarro et al., 2004). As substantial depression seems to be prevalent in 50% of schizophrenic patients (Siris, 1995), for an adequate interpretation of CDSS scores in schizophrenia the score distribution in clinically non-depressed and non-psychotic subjects should be considered. Somehow different to positive and—to a lesser degree-negative symptoms, single depressive symptoms are rather frequent in the general population and depression severity scores seem to be continuously distributed according to a quantitative gene-environment interaction effect (Lesch, 2004).
Section snippets
Design
154 healthy subjects were recruited as controls from four yet unpublished studies on schizophrenia and the validation of the CDSS. All subjects gave informed consent prior to the study. All studies were approved by the local ethics committee.
Participants and assessment
An extensive psychiatric interview and a medical examination took place. The psychiatric assessment comprised a diagnostic interview according to DSM-IV and ICD-10 (DIPS) and standardized rating scales. Subjects with a lifetime diagnosis of affective or
Results
Mean age (32.8 ± 11.7 years, range 18–73 years), and education (mean 11.0 ± 1.7 years, range 8–13 years) were comparable in males and females (48.7% female, n = 75). Table 1 and Fig. 1 present results of descriptive analyses, gender differences, and age-dependence of CDSS items and total scores. Total CDSS scores and single item scores were negatively correlated with age, i.e. higher depression scores were found in younger subjects. Correlation coefficients reached only values of r < 0.30 indicating
Discussion
The study provides psychometric properties and reference values of the CDSS in healthy subjects with low mean depression severity. The nine items of the CDSS comprise a highly sensitive, one-dimensional scale with high internal consistency in healthy subjects corroborating findings in schizophrenic samples (Addington et al., 1992, Addington et al., 1993, Addington et al., 1996, Lancon et al., 1999, Müller et al., 1999). Gender differences were only marginal, and no substantial effect of age and
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