Heightened stress sensitivity is a common characteristic of schizophrenia and may be predictive of clinical and functional outcomes. However, systematic assessment is not part of routine clinical practice. This study investigated the reliability and predictive values of two versions of a new scale for the assessment of psychological stress in psychosis (Psychological Stress Index; PSI). Thirty-seven patients with schizophrenia/schizoaffective disorder and 30 healthy controls completed a battery of self-report measures at baseline and 4-8 weeks for test-retest. Thirty-four patients were followed up at 12 months. Both of the 18-item and 9-item PSI demonstrated good levels of reliability and could significantly discriminate patients from healthy controls. Both versions showed moderate convergence with self-report and clinician ratings of depression and anxiety, and superior predictive validity of 12-month follow-up clinical and functional outcomes compared to an existing measure of stress (Perceived Stress Scale). The clinical usefulness of the PSI is supported by its predictive power on cross-sectional and longitudinal outcome. The PSI-9 performed as well as, if not better than, the PSI-18 in this study, but further evaluation is warranted for more conclusive comparison.
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