Objective: To develop a disease-specific questionnaire to capture the impact of irritable bowel syndrome (IBS) and its treatment on patients' lives, the Irritable Bowel Syndrome Impact Scale (IBS-IS).
Patients and methods: One hundred and fifty-five IBS patients participated (126 (81%) female; age (mean+/-SD) 45.5+/-12.4 years). We developed the initial 39 items from the literature, available IBS-specific instruments and input from physicians, nurses and patients. We deleted IBS-IS items with a high ceiling effect, items that measured a different construct and items showing a high correlation (r>0.90) with another item and with Rasch analysis, leaving 26 items. We then applied exploratory factor analysis to examine domain groupings. Subjects completed the IBS-IS instrument, the Gastrointestinal Symptom Rating Scale for IBS (GSRS-IBS), Short Form-36 (SF-36), Visceral Sensitivity Index (VSI), and Hospital Anxiety and Depression (HAD) scale. Internal consistency, construct validity and discriminate validity were assessed.
Results: The 26 items represented five domains: fatigue, impact on daily activities, sleep disturbance, emotional distress and eating habits. The internal consistency reliability for the domains was 0.87 to 0.96. Most associations between similar constructs in the IBS-IS, GSRS-IBS, SF-36, VSI, and HAD were >0.40. Each IBS-IS domain score decreased with increasing IBS symptom severity (P<0.05), and the patients scored >5 score units lower than a US general population scored on all eight SF-36 dimensions.
Conclusion: The IBS-IS is a short, user-friendly instrument with excellent psychometric properties that has potential usefulness for clinical trials.