Responsiveness and minimal important score differences in quality-of-life questionnaires: a comparison of the EORTC QLQ-C30 cancer-specific questionnaire to the generic utility questionnaires EQ-5D and 15D in patients with multiple myeloma

OBJECTIVES: The aims of this study were to (i) compare the responsiveness of the EORTC QLQ-C30 cancer-specific questionnaire and the generic questionnaires EQ-5D and 15D used for economic evaluation of healthcare interventions and (ii) determine the minimal important differences (MIDs) in these questionnaires. The MID is the smallest change in a quality-of-life score considered important to patients. Methods: Between 2006 and 2008, 239 patients with multiple myeloma completed the questionnaires at inclusion (T1) and after 3 months (T2). At T2, patients were asked whether they had noticed any change in their quality of life. Responsiveness and MIDs were determined by mean score changes (T2-T1) for patients who, in the interview, stated they had improved, deteriorated, or were unchanged. Responsiveness was also assessed using standardized response means. Wilcoxon tests for pair differences were used to evaluate the statistical significance of the changes. Results: Patients who improved had significantly (P < 0.01) higher scores at T2 in all three questionnaires. Patients who deteriorated reported lower scores at T2; however, for the 15D, the differences in score were not statistically significant. The MIDs for the QLQ-C30, EQ-5D, and 15D were 8, 0.08, and 0.03 in patients who improved and 12, 0.10 and 0.02 in patients who deteriorated, respectively. Conclusions: All three questionnaires showed an acceptable responsiveness in patients who improved. However, the 15D did not respond optimally in patients who deteriorate and cannot be recommended for use in patients with myeloma.