Validation of the inflammatory bowel disease disability index for self-report and development of an item-reduced version

Background and aim: The Inflammatory Bowel Disease Disability Index (IBD-DI) is a measure of disability in inflammatory bowel disease (IBD). The IBD-DI is validated for use as a clinical interview but not for use as a self-report questionnaire. We aimed to validate the IBD-DI for self-report (IBD-DI-SR) and to reduce the number of items, using IBD patients from two centers.

Methods: Between April and August 2017, ambulatory IBD patients were recruited from Christchurch Hospital, New Zealand and Concord Hospital, Australia. The IBD-DI clinical interview version was compared with a self-report version. Participants were randomized to do the clinical interview or self-report first. Validation of the IBD-DI-SR involved calculating the correlation coefficient between the clinician completed and self-reported version of the IBD-DI and Cronbach's α of internal consistency of the IBD-DI-SR. To create an item-reduced version, multiple linear regression was used. The R² of the model described the overall association between the item-reduced IBD-DI-SR and the IBD-DI.

Results: One hundred fourteen patients (57 from Christchurch and 57 from Sydney) completed the IBD-DI-SR validation phase, of whom 63 had Crohn's disease and 51 had ulcerative colitis. The Pearson correlation coefficient between the IBD-DI-SR and IBD-DI is 0.90 (P < 0.001), and Cronbach's α of the IBD-DI-SR was 0.86. The item-reduced version of the IBD-DI-SR consisted of eight questions instead of 28, explaining 77% of the variance.

Conclusions: The IBD-DI-SR has demonstrated reliability and validity. The item-reduced IBD-DI-SR is a concise self-report instrument for measuring IBD disability, which makes the IBD-DI more widely usable.