Discriminant and convergent validity of the GSRS-IBS symptom severity measure for irritable bowel syndrome: a population study

Background: The Gastrointestinal Symptom Rating Scale-Irritable Bowel Syndrome (GSRS-IBS) is a 13-item measure of IBS symptom severity. The scale has been used in several studies, but its psychometric properties have been insufficiently investigated and population-based data are not available. Objective: The objective of this article is to establish the factor structure and discriminant and convergent validity of the GSRS-IBS. Methods: The study was based on a Swedish population sample (the Popcol study), of which 1158 randomly selected participants provided data on the GSRS-IBS. We used confirmatory factor analysis (CFA) and compared total and subscales scores in different groups, including IBS diagnostic status, treatment-seeking behavior, and predominant bowel habits. The GSRS-IBS scores were also correlated with quality of life indexes. Results: The sample included 164 participants with a confirmed Rome III IBS diagnosis and 994 participants without the disease. The CFA confirmed the subscales with one exception, in which the incomplete bowel-emptying item belonged to the constipation subscale rather than the diarrhea subscale. The GSRS-IBS total score and subscales were associated with diagnostic status, treatment-seeking behavior, and quality of life dimensions. The relevant subscales scores also differed between the diarrhea- and constipation-predominant subtypes of IBS. Conclusion: The GSRS-IBS total score and subscales have high discriminant and convergent validity. The CFA confirmed the overall validity of the subscales but suggest that a sense of incomplete emptying belongs to the constipation rather than the diarrhea symptom cluster. We conclude that the GSRS-IBS is an excellent measure of IBS symptom severity in the general population.