Factor Structure and Psychometric Properties of the Intolerance of Uncertainty Scale-12 in Multiple Sclerosis

Despite the high prevalence of anxiety disorders in multiple sclerosis (MS) and the inherent uncertainty associated with the disease, it is unclear whether current measures of intolerance of uncertainty (IU) are appropriate for people with MS. In this study, we describe the psychometric features of the short-form Intolerance of Uncertainty Scale (IUS-12) in a mixed sample of 2,084 participants (244 MS, 1,840 non-MS controls). A bifactor model best represented the IUS-12 in the MS group. The IUS-12 appeared suitable in MS, demonstrating good construct validity and moderate test–retest reliability over the 6-month survey period. Measurement invariance was found across MS and non-MS participants. Of note, IU scores were comparable between groups, but IU showed stronger associations with anxiety-related pathologies in participants with MS than non-MS controls. Routine assessment incorporating the IUS-12 may help clarify factors underpinning anxiety and inform the development of targeted psychological interventions for people with MS.