From the Intolerance of Uncertainty Scale–5 to the Intolerance of Uncertainty Scale–4: Psychometric Evaluation and Refinement of an Ultra-Brief Intolerance of Uncertainty Scale in a Sample of Spanish Adults

Background: Intolerance of uncertainty (IU) is a central transdiagnostic vulnerability factor across emotional disorders. However, currently available scales present important limitations, particularly excessive length and factorial instability. Methods: This study evaluated the psychometric properties of the Intolerance of Uncertainty Scale–5 (IUS-5) in a sample of Spanish adults (n = 998) using a cross-sectional online study design with a cross-validation approach that included exploratory graph analyses, redundancy testing, confirmatory factor analyses, and assessments of reliability and convergent validity. Results: Network analyses supported a unidimensional structure but identified item redundancy. Confirmatory analyses indicated that a four-item model (IUS-4) provided the best fit to the data. The IUS-4 demonstrated adequate internal consistency (ω = 0.79), satisfactory convergent validity at the construct level (average variance extracted [AVE] = 0.53), moderate to large correlations with anxiety sensitivity (r = 0.53), and moderate correlations with anxiety, depressive, and obsessive–compulsive symptoms (r = 0.41–0.42). Conclusions: These findings support the IUS-4 as a brief, psychometrically robust, unidimensional measure of IU in the Spanish population. Further research is warranted to examine its applicability in clinical samples and its potential utility as a screening tool.