Development and Validation of a DSM-5-Based Self-Report Screening Tool for Illness Anxiety Disorder

Illness Anxiety Disorder (IAD) is defined in the DSM-5 as involving a persistent preoccupation with having or acquiring a serious illness despite minimal or no somatic symptoms. High levels of health-related anxiety and maladaptive behaviors like excessively seeking medical reassurance or avoiding healthcare are associated with IAD (American Psychological Association, 2013). The current study aims to develop the Illness Anxiety Disorder Scale (IADS), which is a unidimensional, DSM-5-based self-report measure for IAD. Instead of being a diagnostic tool, this scale is meant to be used as a screening tool to identify people who possibly have IAD so that they can be further evaluated for diagnosis. Item Response Theory, which is a modern framework that models the likelihood of endorsing an item based on both a person’s level of the latent trait being measured and the item’s characteristics, was applied to evaluate item functioning and scale properties. The IADS was administered to 241 people. The results revealed that the IADS has a one-factor structure, and the 29 items behave in parallel with fundamental IRT assumptions. Most items demonstrated moderate to high discrimination, and the difficulty parameters also exhibited good distribution, reflecting coverage from moderate to severe symptom levels. Also, information functions showed that the scale is most accurate when the illness anxiety level is moderate to severe; however, there was a lack of measurement precision for lower levels of IAD. These findings suggest that the IADS has a strong potential to be a psychometrically sound screening instrument for IAD.