Psychometric Analysis of the Abdominal Score From the Diary for Irritable Bowel Syndrome Symptoms-Constipation Using Phase IIb Clinical Trial Data

Coon CD1, Hanlon J2, Abel JL3, Lundy JJ4, Carson RT3, Reasner DS5. Value Health. 2020 Mar;23(3):362-369. doi: 10.1016/j.jval.2020.01.002. Epub 2020 Feb 20.


Author information

1 Outcometrix, St Petersburg, FL, USA.

2 Ironwood Pharmaceuticals, Inc, Boston, MA, USA.

3 Allergan plc, Madison, NJ, USA.

4 Outcometrix, St Petersburg, FL, USA. Electronic address: jlundy@outcometrix.com.

5 Imbria Pharmaceuticals, Boston, MA, USA.


OBJECTIVES: The Diary for Irritable Bowel Syndrome Symptoms-Constipation (DIBSS-C) has been developed to assess the core signs and symptoms of irritable bowel syndrome with constipation (IBS-C). This article presents the psychometric evaluation of the DIBSS-C abdominal score.

METHODS: Data for these analyses are from a multicenter phase IIb study in IBS-C patients (NCT02559206). Subjects completed a number of assessments via handheld electronic diary throughout the study. The analyses used the intent-to-treat population and were blinded to randomized treatment group. The analyses evaluated the reliability, validity, and responsiveness of the DIBSS-C abdominal score; identified an appropriate scoring algorithm; and determined thresholds for interpreting clinically meaningful changes at the individual level.

RESULTS: The correlations between the DIBSS-C abdominal symptom items (ie, abdominal pain, discomfort, and bloating) were strong (>0.75). Cronbach's alpha for the abdominal symptom severity items was very strong (.94), indicating that the 3 abdominal symptom items produce a reliable score. The intraclass correlation coefficient for the abdominal score was 0.82, exceeding the threshold of 0.70 and indicating good test-retest reliability. Guyatt's responsiveness statistic values all exceeded the threshold for a large effect of 0.80, so the DIBSS-C abdominal score can be considered highly responsive to change. Triangulation across 3 sets of anchor-based analyses indicated that a threshold of -2.0 points on the abdominal score is an appropriate threshold for identifying meaningful change.

CONCLUSIONS: Overall, this study provides evidence that the DIBSS-C abdominal score is valid, reliable, responsive to change, and interpretable for assessing treatment benefit in patients with IBS-C.

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