Quality of life in functional dyspepsia: responsiveness of the Nepean Dyspepsia Index and development of a new 10-item short form

Background: The Nepean Dyspepsia Index is a reliable and valid measure of quality of life in functional dyspepsia, but responsiveness has been little studied. The Nepean Dyspepsia Index originally contained 42 items designed to measure impairment of a subject's ability to engage in relevant aspects of their life because of dyspepsia, and their enjoyment of these aspects; in addition, the individual importance of areas was assessed. It was subsequently shortened to 25 items, yielding five sub-scales. Aim: To test the Nepean Dyspepsia Index's responsiveness and develop a responsive, very short form. Methods: A randomized, double-blind controlled trial was performed in 589 patients with documented functional dyspepsia. Symptoms and quality of life were measured at baseline, 2 and 4 weeks. Responsiveness of the Nepean Dyspepsia Index quality-of-life section was evaluated by correlation with symptom scores and calculation of standardized changes in scores. Two items from each sub-scale which best represented the area of life (by factor loadings) were selected to create the 10-item short form (SF; short form-Nepean Dyspepsia Index). Internal consistency was assessed by Cronbach's alpha and responsiveness was assessed as above. Results: The Nepean Dyspepsia Index quality-of-life scales demonstrated excellent responsiveness to change in both the active and placebo arms (standardized response means all > 1.0). The Nepean Dyspepsia Index accounted for only 8% of the variance in percentage change in symptoms (by visual analogue scales), indicating that it was evaluating areas of life not covered by symptoms. The 10-item short form had adequate internal consistency (all scales greater than or equal to 0.70) and all strongly (and significantly) correlated with the long form sub-scales; it was also highly responsive. Conclusion: The Nepean Dyspepsia Index is a responsive disease-specific quality-of-life measure; the 10-item short form can be applied in clinical trials of functional dyspepsia.