Validation of the GSFQ, a Self‐Administered Symptom Frequency Questionnaire for Patients with Gastroesophageal Reflux Disease

BACKGROUND: Although the diagnosis of gastroesophageal reflux disease (GERD) is based primarily on symptoms experienced by a patient, relatively little attention has been paid to the development and validation of self-administered questionnaires specific to GERD symptoms. The present article presents the validation of the short, self-administered GERD Symptom Frequency Questionnaire (GSFQ). METHODS: Patients with GERD participating in a randomized clinical trial comparing pantoprazole and nizatidine were asked to complete the GSFQ together with validated instruments for measurement of health-related quality of life (Medical Outcome Study Short Form 12) and gastrointestinal symptoms (Gastrointestinal Symptom Rating Scale). Completion of the GSFQ, Medical Outcome Study Short Form 12 and Gastrointestinal Symptom Rating Scale took place upon entry into the trial (baseline) and during the trial (days 7 and 28). Endoscopy was performed at baseline and after 28 days. Cronbach alpha was used to assess the internal consistency of the questionnaire. The test-retest reliability of the GSFQ was examined by the intraclass correlation coefficient among the 36 patients with stable GERD symptoms between day 7 and day 28. Construct validity was assessed by comparing the GSFQ with previously validated instruments. Known group validity was determined by comparing GSFQ scores across groups of patients known to differ clinically. Responsiveness to change was assessed by the Guyatt's statistic. RESULTS: Two hundred twenty-one patients formed the study baseline group. The analysis demonstrated that the GSFQ questionnaire had excellent psychometric properties shown by the high internal consistency (Cronbach alpha 0.84); that the test-retest reliability was satisfactory (intraclass correlation coefficient 0.64); that there was good evidence that the GSFQ indeed measured what it was intended to measure (validity); and that the GSFQ was highly responsive to change (Guyatt's statistic 1.48). DISCUSSION: The GSFQ is a short, self-administered, easy to use, GERD-specific questionnaire which should be considered as a useful assessment tool in the evaluation of patients with GERD and in the assessment of treatment outcomes.