Objective: We describe the validation of a German-language version of the Reflux Disease Questionnaire in what is the first validation study of this patient questionnaire for a non-English speaking population. Gastro-oesophageal reflux disease is one of the most common diseases in primary care and has a significant negative impact on patients' quality of life. There is no gold standard for diagnosing gastro-oesophageal reflux disease, however, so the valid assessment of symptoms is especially important.
Design and methods: A total of 5689 patients (92%) completed the questionnaire both before treatment and after 2 weeks. The results were tested for validity and reliability. Predictive validity was tested in a pilot study of 100 patients. Convergent validity was examined using the Quality of Life in Reflux and Dyspepsia Questionnaire for the assessment of disease-specific quality of life and the McMaster Overall Treatment Evaluation for the assessment of therapeutic success.
Results: Principal component analysis suggested a three-factor solution with the subscores heartburn, regurgitation, and dyspepsia. The internal consistencies of the subscores were between 0.84 and 0.86. Item difficulty ranged from 0.33 to 0.53, and corrected item-total correlation from 0.66 to 0.72. Effect sizes were between 0.8 and 1.0.
Conclusion: The German version of the questionnaire has good psychometric properties and is responsive to changes in health. Thus, we conclude that the German Reflux Disease Questionnaire is suitable for the assessment of heartburn, regurgitation, and treatment response, both in primary care settings and clinical studies.