[Clinical assessment of schizophrenic syndrome (CASS): validity evaluation of the new diagnostic tool]

The aim of the study was an evaluation of validity measures of the CASS (Clinical Assessment of Schizophrenic Syndromes)--a new multi-purpose and multi-level clinical diagnostic instrument consisting of a diagnostic questionnaire (CASS-D) allowing to analyze a diagnosis of schizophrenia according to DSM-IV and ICD-10 criteria as well as of three rating scales designed for description and intensity evaluation of schizophrenic syndromes on the global (CASS-G), dimensional (CASS-P, a profile of 13 basic dimensions) or symptomatological (CASS-S, a set of 31 symptoms) level.

194 inpatients consecutively admitted to the Department within approximately 6 months were assessed twice (at the start and end of their hospitalization) by 12 trained diagnosticians.

Several measures of validity were analyzed. Results obtained by means of CASS were compared with results of the SANS/SAPS, BPRS, and PANSS as reference rating scales (diagnostic validity). Characteristics of frequency, intensity, dynamics and specificity of scale items were used to analyze content validity. Factorial structure of CASS scales was applied as a measure of construct validity.

Diagnostic validity of the new instrument seems to be confirmed by its very high correlation coefficients with rating scales recognized as international standards: BPRS, PANSS, and SANS/SAPS. Reasonable characteristics of frequency, intensity, dynamics and specificity of individual items (dimensions, symptoms) and sum scores of CASS scales and relationships between their values strongly suggest their content validity. Both sum (CASS-P, CASS-S) and global (CASS-G) scores of scales under study revealed some specificity--they had significantly higher values in patients with schizophrenia than in patients with other diagnoses. It allows to distinguish in a schizophrenic syndrome described by CASS components which are specific and not specific for this disorder. The latter have been left also in the final version for their practical and clinical importance. Construct validity of the CASS was studied separately for different scales (CASS-P, CASS-S) and different groups (all or only schizophrenic patients) by means of several factor analyses, and performed along identical statistical procedure (principal component method of extraction with criterion eigenvalue > 1, followed by Equamax rotation). Resulting solutions could be interpreted reasonably and consistently with contemporary attempts to find adequate factorial models of intrinsic structure of schizophrenic syndrome. Thus they support confidence for constructive aspect of the CASS validity.

Ultimately, results obtained in the study suggest that the CASS may be considered as an instrument with some promising indices of diagnostic, content and construct validity, which may be potentially useful for clinical and research purposes.