Rasch analysis of the Incontinence Impact Questionnaire short version (IIQ-7) in women with urinary incontinence

Urinary incontinence is a clinical condition that can negatively affect activities, psychosocial well-being, and health-related quality of life. The Incontinence Impact Questionnaire short version (IIQ-7) is useful to quantify quickly the urinary incontinence-related life-impact. Previous psychometric studies on the IIQ-7, using classical test theory methods, demonstrated good internal consistency, test-retest reliability, and a substantial unidimensionality of the tool. This latter property is a prerequisite for performing advanced modern psychometric analyses such as Rasch analysis. In this study, we aimed to examine in depth - through Rasch analysis - some key metric properties of the IIQ-7. We analyzed data from 100 women with urinary incontinence. Results confirmed the correct functioning of the four response categories of the questionnaire and indicated an adequate level of internal structural validity. Given the good fit of the items to the Rasch model, it was possible to obtain a nomogram to transform the total raw scores of the IIQ-7 into linear measure estimates. Our findings obtained through Rasch analysis confirm the substantial unidimensionality and good psychometric properties of the IIQ-7 found in previous studies. They enhance the confidence in the use of this short tool - for group-level decisions - to assess the life-impact related to stress, urge or mixed urinary incontinence among women.