Objective: To describe the process followed for the cultural and psychometric adaptation (validation) to Spanish of the Gastrointestinal Short Form Questionnaire (GSFQ), used to measure the interference of symptoms of gastroesophageal reflux disease GERD and to report the psychometric properties of this instrument.
Material and methods: The adaptation process was supervised by a five-member expert panel. After forward and backward translations in duplicate, a Spanish version was obtained, which was administered to two samples; a five-patient pilot sample to check comprehension and face validity, and a 4,000-patient sample to check structural validity (factor analysis and reliability), construct validity, and discriminative validity.
Results: The questionnaire showed a unique dimension that matched that of the original questionnaire. Reliability was high (alpha=0.83), and the correlation between even-odd items was good (r=0.69). The overall score correlated with generic health-related quality of life measures evaluated by the EQ-5D tariff (r=0.499) and VAS (r=-0.481). The scale discriminated between GERD severity levels (p<0.008) as measured by the Savary-Miller scale, except for the most severe level with respect to the levels immediately below. The questionnaire was able to detect differences between diverse concomitant diseases and antecedents. Sensitivity with respect to the GERD clinician criterion was 60.5% and specificity was 68.3%. Normative comparison scaling values are reported.
Conclusions: The results show acceptable psychometric properties. A new instrument to assess the interference of GERD symptoms is thus available to health professionals. This instrument takes the patient's perspective into account.