Validation of the IBD-Control Questionnaire across different sociodemographic and clinical subgroups: secondary analysis of a nationwide electronic survey

Background: The IBD-Control Questionnaire is a simple, generic measure of patient-perceived disease control used increasingly in clinical practice and research. We aimed to address knowledge gaps in its psychometric performance, to ensure that it can be used with confidence in a variety of contexts. Methods: We analysed 7341 responses to the IBD Registry COVID-19 survey, sent to 40 911 patients who completed an online self-assessment tool during the pandemic. Questions covered demographics, comorbidities, inflammatory bowel disease [IBD] sub-type, and IBD-Control Questionnaire and symptom scores [CD-PRO2 or UC-PRO2]. Psychometric properties of IBD-Control-8 were tested overall and within subgroups (Crohn's disease [CD], ulcerative colitis [UC] and IBD unclassified; male and female; <= 65 and >65 years; number of co-morbidities; deprivation status). Results: Internal consistency was very strong overall [alpha: 0.84, omega: 0.89] and for each subgroup [alpha range: 0.81-0.85; omega: 0.86-0.90]. Construct validity was demonstrated by moderate correlation of each item with global rating [VAS] [r s range: 0.47-0.65], strong correlation between IBD-Control-8 score and VAS [r(s) = 0.74], moderate-to-strong with PRO2 scores [CD: r(s) = -0.718; UC: r(s) = -0.602] and significantly higher IBDControl-8 scores for PRO2-remission vs PRO2-active, consistent across subgroups. Exploratory and confirmatory factor analyses demonstrated a two-factor model (items loading onto 'Health-related Quality of Life' [HRQoL] or 'Treatment' domains). Extensive tests for factorial invariance confirmed consistency. Conclusions: IBD-Control-8 is a psychometrically robust scale which can be used across a range of populations. It offers a quick, reliable, and valid method of assessing patient-perceived control. The construct of 'control' includes traditional HRQoL and a novel domain relating to treatment perception.