In our earlier studies the Paranoid Depressivitäts-Skala (PD-S) designed by von Zerssen to measure schizophrenic patients' mental state was found to have a high reliability, specific validity and limited practical usefulness. In order to improve its practical usefulness we proposed to shorten the original scale on the grounds of a secondary, retrospective psychometric analysis. This turned out to be feasible, with the psychometric properties of the original retained.
Aims – In the present prospective study psychometric properties of the shortened version of the scale (sPD-S) were assessed directly.
Subjects – 41 patients diagnosed with various mental disorders (in that number 23 patients with the diagnosis of schizophrenia according to the ICD-10) were examined using the sPD-S.
Method – The Clinical Assessment of Schizophrenic Syndromes (CASS) both in the .full version of the CGI type (CASS-C) and in that describing basic clinical dimensions of the psychopathological syndrome (CASS-W) were used as alternative instruments of clinical diagnosis. The patients self-rated their mental state every week, while psychiatrists assessed the patients' state every two to four weeks.
Results – The sPD-S may be used reliably – the tool indicates a very high internal consistency and test-retest stability. However, its validity seems to be specific and only slightly related to the clinical diagnosis. The best approximation of the scale factorial structure seems to be a two-dimensional solution (depressive experiences and paranoid experiences) corresponding to what was intended by the author of the original tool. The scale reliability and factorial structure were stable over successive weeks, despite changes in the patients' mental state. Besides, the scale turned out to be less tiresome for the patients who were more willing to co-operate. Thus, the sPD-S as compared to the full scale seems to be more useful in clinical practice, especially if it is to be used repeatedly.
Discussion – The results of the direct evaluation of the sPD-S psychometric properties are in agreement with the conclusions drawn from our earlier; secondary evaluation of the scale.
Conclusions – The sPD-S may be useful for monitoring changes in the patients' self-rating of their mental state.