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

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.

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.

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.

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.