Abstract
INTRODUCTION: The instruments used for the clinical assessment of schizophrenia and other psychotic disorders are not commonly administered in routine clinical practice since their application takes a long time. This study aims to develop a short, comprehensive, and easy-to-apply scale and to examine its psychometric properties. METHODS: A 14-item scale was prepared by adding two items inquiring about obsessions and memory difficulties to the items taken from Positive and Negative Syndrome Scale (PANSS) covering the diagnostic criteria for schizophrenia and schizoaffective disorder. The items were rated on a 4-point scale reflecting their effect on daily functioning as 1. not present, 2. mild problems, 3. moderate problems, 4. severe problems. The scale was administered together with other concordant scales to the patients with schizophrenia and schizoaffective disorder. The construct validity of the scale was analyzed by explanatory factor analysis, the concurrent validity was examined through correlations of the scale scores with those of comparable scales, and criterion validity was evaluated by the sensitivity to the change in psychopathology. For reliability, internal consistency coefficient and interrater reliability were assessed. RESULTS: Data from a total of 120 patients were analyzed. The internal consistency coefficient of the scale was calculated as 0.89. Exploratory factor analysis yielded a 4-factor solution which accounted for 74.47% of the total variance of the scale scores. The first factor (psychosis) explained 43.49% of the total variance, the second factor (negative/cognitive impairment) explained 14.53%, the third factor (emotional distress) explained 11.19%, and the fourth factor (disorganization) explained 5.34% of the total variance. Significant correlations were found between the scale's total score and the PANSS (r=0.78), Clinical General Impression-Severity (CGI-S) (r=0.81), and Global Assessment of Functioning (GAF) scores (r=-0.77). Interrater reliability was strong (ICC=0.89), and the sensitivity to the change in psychopathology was significant (Cohen d=2.68). CONCLUSION: The scale demonstrated adequate psychometric properties in terms of reliability, validity, and dimensionality that justify its use in routine clinical practice.