Psychometric properties of the Overall Anxiety Severity and Impairment Scale (OASIS) among psychiatric outpatients

•The OASIS is a valid and reliable measure of anxiety severity and related impairment in multiple settings.•The OASIS has a unidimensional factor structure.•The OASIS is able to determine illness severity.

BackgroundThe Overall Anxiety Severity and Impairment Scale (OASIS) is a brief, transdiagnostic measure used to assess anxiety severity and related interference. The OASIS has demonstrated strong psychometric properties in previous investigations, however, it has yet to be validated using a transdiagnostic clinician-rated measure.MethodsWe evaluated the factor structure, convergent and discriminant validity, and illness severity cut-scores of the OASIS in a sample of outpatients (N=202).ResultsA confirmatory factor analysis indicated an unidimensional structure provided the best fit. The OASIS demonstrated good convergent validity and internal consistency. Using the Clinical Global Impression-Severity Scale (CGI-S), ROC curves showed OASIS scores of 6, 10 and 12 to indicate moderate, marked and severe illness severity, respectively.ConclusionsThe OASIS is a unidimensional self-report measure with good convergent validity and data from the current study provide illness severity cut-scores.