Clinical Trials Study
Copyright ©The Author(s) 2015. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Jan 7, 2015; 21(1): 292-300
Published online Jan 7, 2015. doi: 10.3748/wjg.v21.i1.292
Latent structure of irritable bowel syndrome symptom severity
Fabian Jasper, Boris Egloff, Andrea Roalfe, Michael Witthöft
Fabian Jasper, Department of Psychological Diagnostics, University of Salzburg, 5020 Salzburg, Austria
Boris Egloff, Department of Personality Psychology and Diagnostics, University of Mainz, 55099 Mainz, Germany
Andrea Roalfe, Primary Care Clinical Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
Michael Witthöft, Department of Health Psychology, University of Mannheim, 68161 Mannheim, Germany
Author contributions: All authors contributed equally to this work.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Dr. Fabian Jasper, Department of Psychological Diagnostics, University of Salzburg, Kapitelgasse 5, 5020 Salzburg, Austria. fabian.jasper@sbg.ac.at
Telephone: +49-151-21719210 Fax: +49-151-21719210
Received: June 4, 2014
Peer-review started: June 5, 2014
First decision: July 21, 2014
Revised: August 30, 2014
Accepted: September 29, 2014
Article in press: September 30, 2014
Published online: January 7, 2015
Abstract

AIM: To investigate the latent structure of an irritable bowel syndrome (IBS) symptom severity scale in a population of healthy adults.

METHODS: The Birmingham IBS symptom questionnaire which consists of three symptom specific scales (diarrhea, constipation, pain) was evaluated by means of structural equation modeling. We compared the original 3-factor solution to a general factor model and a bifactor solution in a large internet sample of college students (n = 875). Statistical comparisons of competing models were conducted by means of χ2 difference tests. Regarding the evaluation of model fit, we examined the comparative fit index (CFI) and the Root Mean Square Error of Approximation (RMSEA).

RESULTS: Results clearly favored a bifactor model of IBS symptom severity (CFI = 0.99, RMSEA = 0.05) which consisted of a strong general IBS somatization factor and three symptom specific factors (diarrhea, constipation, pain) based on the subscales of the Birmingham IBS symptom questionnaire. The fit indices of the competing one factor model (CFI = 0.85, RMSEA = 0.17) and three factor model (CFI = 0.97, RMSEA = 0.08) were clearly inferior. χ2 difference tests showed that the differences between the models were indeed significant in favor of the bifactor model (P < 0.001). Correlations of the four latent factors with measures of pain sensitivity, somatoform dissociation, fatigue severity, and demographic variables support the validity of our bifactor model of IBS specific symptom severity.

CONCLUSION: The findings suggest that IBS symptom severity might best be understood as a continuous and multidimensional construct which can be reliably and validly assessed with the B-IBS.

Keywords: Irritable bowel syndrome, Irritable bowel syndrome, Bifactor, Gastrointestinal, Rome-III criteria, Birmingham irritable bowel syndrome scale

Core tip: The findings suggest that irritable bowel syndrome (IBS) symptom severity might best be understood as a continuous and multidimensional construct which can be reliably and validly assessed with the B-IBS questionnaire. The B-IBS scale is suitable to assess therapeutic outcomes of IBS treatments because it can measure IBS symptom severity in both, patients suffering from an IBS and participants who do not fulfill the diagnostic criteria for an IBS diagnosis but do show some of the associated symptoms.