Using Item Response Theory (IRT) to Improve the Efficiency of the Simple Clinical Colitis Activity Index (SCCAI) for patients with ulcerative colitis

Abstract

BackgroundThe SCCAI was designed to facilitate assessment of disease activity in ulcerative colitis (UC). We aimed to interrogate the metric properties of individual items of the SCCAI using item response theory (IRT) analysis, to simplify and improve its performance. MethodsThe original 9-item SCCAI was collected through TrueColours, a real-time software platform which allows remote entry and monitoring of patients with UC. Data were securely uploaded onto Dementias Platform UK Data Portal, where they were analysed in Stata 16.1 SE. A 2-parameter (2-PL) logistic IRT model was estimated to evaluate each item of the SCCAI for its informativeness (discrimination). A revised scale was generated and re-assessed following systematic removal of items. ResultsSCCAI data for 516 UC patients (41 years, SD=15) treated in Oxford were examined. After initial item deletion (Erythema nodosum, Pyoderma gangrenosum), a 7-item scale was estimated. Discrimination values (information) ranged from 0.41 to 2.52 indicating selected item inefficiency with three items <1.70 which is a suggested discriminatory value for optimal efficiency. Systematic item deletions found that a 4-item scale (bowel frequency day; bowel frequency nocturnal; urgency to defaecation; rectal bleeding) was more informative and discriminatory of trait severity (discrimination values of 1.50 to 2.78). The 4-item scale possesses higher scalability and unidimensionality, suggesting that the responses to items are either direct endorsement (patient selection by symptom) or non-endorsement of the trait (disease activity). Conclusion Reduction of the SCCAI from the original 9-item scale to a 4-item scale provides optimum trait information that will minimise response burden. This new 4-item scale needs validation against other measures of disease activity such as faecal calprotectin, endoscopy and histopathology.

Clinical Effect of Mirikizumab Treatment on Bowel Urgency in Patients with Moderately to Severely Active Ulcerative Colitis and the Clinical Relevance of Bowel Urgency Improvement for Disease Remission

“…Monitoring bowel urgency can be achieved with an index that includes urgency as a relevant measure of disease activity such as the Simple Clinical Colitis Activity Index. 52 For those health-care providers who use a UC index such as the SCCAI in their clinic, urgency is being asked about; however, often such indexes are not used clinically, and they can also be prone to bias if the clinician gives an interpretation of the patient's response. 53 The SCCAI includes a question on bowel urgency using a four-point scale that lends itself to remote digital monitoring completed by patients.…”

“…53 The SCCAI includes a question on bowel urgency using a four-point scale that lends itself to remote digital monitoring completed by patients. 52 The United States FDA Draft Guidance 54 for the development of patient-reported outcomes has been updated to include means of measuring urgency. 16 These include the Symptoms and Impacts Questionnaire for UC, 55 Ulcerative Colitis Patient-Reported Outcomes Signs and Symptoms diary, 14 , and the UNRS.…”