Responsiveness to Change and Minimally Important Differences of the Patient-Reported Outcomes Measurement Information System Gastrointestinal Symptoms Scales

The NIH-sponsored Patient-Reported Outcomes Measurement Information System (PROMIS) Gastrointestinal (GI) Symptoms scales were developed to assess patients' GI symptoms in clinical settings. To assess responsiveness to change and provide minimally important difference (MID) estimates for the PROMIS GI Symptoms scales. A sample of 256 GI outpatients self-administered the eight PROMIS GI Symptoms scales (gastroesophageal reflux, disrupted swallowing, diarrhea, bowel incontinence/soilage, nausea and vomiting, constipation, belly pain, and gas/bloating/flatulence) at two visits. Patient self-reported and physician-reported assessments of the subjects' overall GI condition were employed as change anchors. In addition, we prospectively assessed change at both visits using a GI-symptom anchor, the Gastrointestinal Symptom Rating Scale (GSRS). Responsiveness to change was assessed using F-statistics. The minimally changed group was those somewhat better or somewhat worse on the retrospective anchors and changing by one category on the modified GSRS (e.g., from slight to mild discomfort to moderate to moderately severe discomfort). Responsiveness to change was statistically significant for 6 of 8 PROMIS scales using the self-report GI anchor, 3 of 8 scales using the physician-reported anchor, and 5 of 5 scales using the corresponding GSRS scales as anchors. The MID estimates for scales for improvement and worsening were about 0.5-0.6 SD using the GSRS anchor and generally larger in magnitude than the change for the "about the same" group. The responsiveness and MID estimates provided here for the PROMIS GI Symptoms scales can aid in scale score interpretation in clinical trials and observational studies.