Factor structure of the illness intrusiveness rating scale in patients diagnosed with anxiety disorders

The Illness Intrusiveness Rating Scale (IIRS) is a measure designed to assess the impact of illness on various domains of functioning (G. M. Devins, 1994). In anxiety disordered patients, illness intrusiveness ratings are higher than those of chronically ill medical patients, suggesting that the IIRS may have a different underlying structure in a sample of individuals with anxiety disorders. To examine this possibility, IIRS items were submitted to an exploratory and confirmatory factor analysis in 2 samples (total N = 294). These solutions were compared to solutions in chronically ill populations from a previous study. In the exploratory analysis, both a one-factor and a three-factor solution were identified, accounting for 42 and 61 % of the variance, respectively. Confirmatory analyses showed adequate similarity between the three-factor structure of the IIRS from a medically ill population and the current three-factor structure, suggesting that elevated IIRS scores in anxiety disordered samples cannot be explained simply by a different structure of the instrument.