Psychometric properties of the Intolerance of Uncertainty Scale-12 in generalized anxiety disorder: assessment of factor structure, measurement properties and clinical utility

Intolerance of uncertainty is a psychological vulnerability implicated in the development and maintenance of generalized anxiety disorder (GAD). The Intolerance of Uncertainty Scale-12 (IUS-12) is a widely used measure, however no studies have thoroughly tested the psychometric properties in a clinically diagnosed GAD sample. This study aimed to evaluate the factor structure, measurement properties and clinical utility of the IUS-12 in clinical and non-clinical samples. Participants were screened using the Anxiety Disorders Interview Schedule for DSM-IV to ascertain clinical (n = 136: principal diagnosis of GAD) or non-clinical status (n = 76). Confirmatory factor analysis determined that the bifactor type (two-factor testlet) model demonstrated significantly better fit in comparison to the unidimensional model for the clinical sample. The IUS-12 exhibited limited multidimensionality indicating that only the total score provides meaningful interpretation. The IUS-12 demonstrated good construct validity (with DASS-21, MCQ-30, and PSWQ), good internal consistency, as well as good test-retest reliability over 12-weeks. The IUS-12 demonstrated responsivity to treatment following cognitive behavioral therapy and mindfulness based psychological interventions. Receiver operating characteristic curve analysis indicated an optimal cut-off score of 28 for distinguishing individuals with GAD from non-clinical cases. Overall, the IUS-12 is a valid, reliable and clinically useful instrument for individuals with GAD.