THE PREDICTIVE-VALIDITY OF A DIAGNOSIS OF SCHIZOPHRENIA - A REPORT FROM THE INTERNATIONAL STUDY OF SCHIZOPHRENIA (ISOS) COORDINATED BY THE WORLD-HEALTH-ORGANIZATION AND THE DEPARTMENT-OF-PSYCHIATRY, UNIVERSITY-OF-NOTTINGHAM

Background Outcome is important in the validation of psychiatric diagn osis, as most disorders lack clinicopathological correlates. We descri be the predictive validity of four definitions of schizophrenia (DSM-I II-R, ICD-10, ICD-9 and CATEGO S+), in a representative cohort of pati ents selected during their ii rst episode of psychosis. Method Each de finition of schizophrenia was applied to 99 patients. Their respective ability to predict 13-year outcome (Global Assessment of Functioning scales) was assessed. Results DSM-III-R and ICD-10 diagnoses of schizo phrenia have high predictive validity for long-term outcome, and both provide relatively stable diagnoses. ICD-9 is reasonably good at predi cting disability, but not symptoms, and CATEGO S+ showed no predictive validity Adding six-month duration criteria to ICD-10, ICD-9 and CATE GO S+ improved their predictive validity, and removing the six-month d uration criterion from DSM-III-R commensurately reduced predictive val idity Conclusions Modern diagnostic systems (DSM-III-R and ICD-10) hav e high predictive validity, and are superior to ICD-9. The six-month d uration criterion of DSM-III-R schizophrenia accounts for its predicti ve validity and stability over 13 years, but restricts its use in firs t-episode studies. The one-month duration criterion of ICD-10 is less restrictive, without major compromises in predictive validity or stabi lity.