Psychometric evaluation of an Italian custom 4-item short form of the PROMIS anxiety item bank in immune-mediated inflammatory diseases: an item response theory analysis.

backgroundThere has recently been growing interest in the roles of inflammation in contributing to the development of anxiety in people with immune-mediated inflammatory diseases (IMID). Patient-reported outcome measures can facilitate the assessment of physical and psychological functioning. The National Institutes of Health (NIH)'s Patient-Reported Outcomes Measurement Information System (PROMIS®) is a set of Patient-Reported Outcomes (PROs) that cover physical appearance, mental health, and social health. The PROMIS has been built through an Item Response Theory approach (IRT), a model-based measurement in which trait level estimates depend on both persons' responses and on the properties of the items that were administered. The aim of this study is to test the psychometric properties of an Italian custom four-item Short Form of the PROMIS Anxiety item bank in a cohort of outpatients with IMIDs.

methodsWe selected four items from the Italian standard Short Form Anxiety 8a and administered them to consecutive outpatients affected by Inflammatory Bowel disease (

resultsTaken together, Confirmatory Factor Analysis and Exploratory Factor analysis suggest that the unidimensionality assumption of the instrument holds. The instrument has excellent reliability from a Classical Theory of Test (CTT) standpoint (Cronbach's α = 0.93, McDonald's ω = 0.92). The 2PL Graded Response Model (GRM) model provided showed a better goodness of fit as compared to the 1PL GRM model, and local independence assumption appears to be met overall. We did not find signs of differential item functioning (DIF) for age and gender, but evidence for uniform (but not non-uniform) DIF was found in three out of four items for the patient DISCUSSION: The Italian custom four-item short form from the PROMIS anxiety form 8a shows acceptable psychometric properties both from a CTT and an IRT standpoint. The Test Reliability Curve shows that this instrument is mostly informative for people with higher levels of anxiety, making it particularly suitable for clinical populations such as IMID patients.