Impact of irritable bowel syndrome on patientsʼ lives: development and psychometric documentation of a disease-specific measure for use in clinical trials

OBJECTIVETo develop a disease-specific questionnaire to capture the impact of irritable bowel syndrome (IBS) and its treatment on patientsʼ lives, the Irritable Bowel Syndrome Impact Scale (IBS-IS). PATIENTS AND METHODSOne 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. RESULTSThe 26 items represented five domainsfatigue, 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 (P5 score units lower than a US general population scored on all eight SF-36 dimensions. CONCLUSIONThe IBS-IS is a short, user-friendly instrument with excellent psychometric properties that has potential usefulness for clinical trials.