Stability and Change in Intolerance of Uncertainty and Its Association with Interpretation Bias in Social Situations: A Longitudinal Study of Italian Adolescents

Background: Intolerance of Uncertainty (IU) is a transdiagnostic factor measured using the Intolerance of Uncertainty Scale-Revised (IUS-R). This study evaluated the stability and change in adolescents' IU over a three-month period using a modified version of the scale. Methods: A two-wave study was conducted, with 290 adolescents responding to an online survey at baseline and 199 at follow-up. The original IUS-R was modified to probe the rating of the current perceived state of IU, rather than typical experience. The link between IU variability and the development of interpretation bias in ambiguous social situations at follow-up was explored. Structural Equation Modeling and Linear Mixed Model analyses were performed to assess the longitudinal measurement invariance and responsiveness of the Modified IUS-R scale. Results: The scale demonstrated good psychometric properties and full measurement invariance. Individual participants showed significant variability in baseline IU levels but not in the degree of change. A reliable change in scores was observed in 8% of adolescents. The Modified IUS-R predicted interpretation bias in social situations at follow-up. Conclusions: Significant inter-individual-level variation in IU suggests this tool may be useful for detecting changes in IU and predicting significant health outcomes. Future studies should further address the assessment of changing IU with longer timeframes.