Factor structure of the Korean version of illness intrusiveness rating scale: cross-cultural implications

The Illness Intrusiveness Rating Scale (IIRS) measures illness-induced disruptions to 13 domains of lifestyles, activities, and interests. A stable three-factor structure has been well documented; however, the cross-cultural validity of this scale needs to be tested. This study investigated the factor structure of the Korean version of IIRS in 712 outpatients at a university medical center. A predominant diagnosis of the patients was rheumatoid arthritis (47%). The Center for Epidemiological Studies-Depression Scale (CES-D), and Health Assessment Questionnaire (HAQ) were also administered. Exploratory Principal Component Analysis identified a two-factor structure, "Relationships and Personal Development (RPD)" and "Instrumental", accounting for 57% of the variance. Confirmatory analyses extracted an identical factor structure. However, a goodness-of-the fit test failed to support two-factor solution (chi(2)=138.2, df=43, p<.001). Two factors had high internal consistency (RPD, alpha=.89; Instrumental, alpha=.75) and significantly correlated with scores of HAQ (RPD, r=.53, p<.001; Instrumental, .r=44, p<.001) and CES-D (RPD, .r=55, p<.001; Instrumental, .r=43, p<.001). These findings supported construct validity of the Korean version of IIRS, but did not support cross-cultural equivalence of the factor structure.