Multi-Dimensional Gastrointestinal Symptom Severity Index: Validation of a Brief GI Symptom Assessment Tool

Few instruments have been developed and validated for the evaluation of multi-dimensional GI symptoms. The Gastrointestinal Symptoms Severity Index (GISSI), a multi-dimensional, self-report instrument, was designed as a brief measure of the frequency, severity, and bothersomeness of individual GI and pelvic floor/urogynecologic symptoms. Aim To report the psychometric properties of the GISSI subscales, including factorial structure, validity, and internal consistency. Methods The GISSI included 32 items that assessed upper and lower GI symptoms and seven items related to pelvic floor/urogynecologic symptoms. A total of 934 patients presenting for upper and lower GI complaints completed the questionnaire between January 2013 and December 2013. The sample was randomly split into derivation (n=466) and validation datasets (n=468). A non-patient sample of 200 was collected separately. Results Exploratory factor analysis supported a six-factor model for the derivation sample that accounted for 69.3 % of the total variance. The six GI symptom clusters were labeled as constipation/difficult defecation (five items), abdominal pain/discomfort (four items), dyspepsia (four items), diarrhea/anal incontinence (four items), GERD/chest symptoms (four items), and nausea/vomiting (two items). Inclusion of additional items related to female pelvic floor/urogynecologic symptoms resulted in a separate factor. Confirmatory factor analysis of the validation dataset supported the a priori hypothesized six-factor measurement model (X-2(428)=1462.98; P<0.001; GFI=.88; RMSEA=.051). Conclusion The GISSI demonstrated good to excellent psychometric properties and provided multi-dimensional scaling of prominent GI symptom clusters. Further validation may provide an efficient, valid, and reliable measure of patient-reported clinical outcomes.