OBJECTIVE: To evaluate the psychometric properties of the Diary for Irritable Bowel Syndrome Symptoms-Constipation (DIBSS-C), which was developed to support primary and secondary endpoints in irritable bowel syndrome with predominant constipation (IBS-C) clinical trials.
METHODS: Observational data were collected from 108 adults with IBS-C using a smartphone-type device for 17 days. DIBSS-C data regarding bowel movements (BMs) were collected for each event (along with the Bristol Stool Form Scale [BSFS]); abdominal symptoms were rated each evening. Global status items and the Gastrointestinal Symptom Rating Scale-IBS (GSRS-IBS) were completed on Day 10 and Day 17 and the IBS-Symptom Severity Scale (IBS-SSS) on Day 17. Item-level performance, internal consistency reliability, test-retest reliability, and construct validity were evaluated.
RESULTS: The Abdominal Symptoms Domain score demonstrated high internal consistency reliability (Cronbach's alpha Week 1 = 0.98; Week 2 = 0.96) and test-retest reliability (intraclass correlation coefficient [ICC] = 0.93). Test-retest reliability was stronger for abdominal symptoms (ICC = 0.91 - 0.94) than for the frequency-based BM-related outcomes (ICC = 0.54 - 0.66). Key construct validity hypotheses were supported by moderate to strong correlations with the corresponding GSRS-IBS, IBS-SSS, and BSFS items. All known-groups comparisons were statistically significant for the abdominal symptom items and domain score; evidence for known-groups validity of BM-related outcomes was supportive when based on constipation severity.
CONCLUSIONS: The results of this study provided key psychometric evidence for the DIBSS-C, ultimately contributing to its qualification by the US Food and Drug Administration for use in IBS-C clinical trials.
