Structure of lifestyle disruptions in chronic disease - A confirmatory factor analysis of the illness intrusiveness ratings scale

BACKGROUND. The Illness Intrusiveness Ratings Scale MRS) measures the exten t to which disease or its treatment or both interfere with activities in im portant life domains. Before comparing IIRS scores within or across groups it is crucial to determine whether a common underlying factor structure exi sts across patient populations. OBJECTIVE. To investigate the factor structure underlying the IIRS. and eva luate its stability across diagnoses. METHODS. IIRS responses from 5,671 respondents were pooled from 15 separate studies concerning quality of life in eight patient groups: rheumatoid art hritis; osteoarthritis; systemic lupus erythematosus; multiple sclerosis; e nd-stage renal disease (maintenance dialysis); renal transplantation; heart , liver, and lung transplantation; and insomnia. Data were gathered by diff erent methods (eg, interview, self-administered, mail survey) and in divers e contexts (eg, individual vs. group). RESULTS. Exploratory maximum-likelihood factor analysis identified three un derlying factors in a randomly selected subset of respondents (n = 400), co rresponding to "Relationships and Personal Development," "Intimacy," and "I nstrumental" life domains. Confirmatory factor analysis corroborated the st ability of this structure in an independent subsample (n = 2100). Complemen tary goodness-of-fit indices confirmed the consistency of the three-factor solution, corroborating that IIRS scores are uniquely defined across patien t populations. Coefficient alpha was high for total and subscale scores. CONCLUSIONS. IIRS scores can be compared meaningfully within and across pat ient groups. Both total and subscale scores can be used depending on resear ch objectives.