Using the EuroQol EQ-5D in Swiss cancer patients, which value set should be applied?

Background: The European Quality of Life-5 Dimensions (EQ-5D) instrument combines questionnaire responses into a single utility estimate using country-specific value sets. Countries without a national value set are advised to select one based on geographic proximity. In the absence of a Swiss value set, we used foreign value sets to gain insights into their appropriateness for use with Swiss cancer patients.

Methods: EQ-5D health states and visual analogue scale (VAS) ratings were collected in one German and three Swiss oncology trials. Utilities were calculated based on the United Kingdom (UK), German (GE), French (FR) and European Union (EU) value sets. Resulting differences and Pearson partial correlation coefficients with corresponding VAS ratings were assessed.

Results: In total, 202 Swiss and 154 German patients undergoing cancer treatment completed at least two EQ-5D forms. The mean difference between GE-based and FR-, UK- or EU-based utilities was significantly larger than the differences between the latter. The absolute mean difference between utilities and VAS ratings was highest for GE-based utilities, for Swiss (0.170, 95 % confidence interval [CI] 0.146-0.194) and German patients (0.174, 95 % CI 0.145-0.202). The correlation between GE-based utilities and VAS ratings was the lowest (r = 0.36, 95 % CI 0.33-0.40); the highest was between FR-based utilities and VAS ratings (r = 0.43, 95 % CI 0.39-0.46).

Conclusion: For Switzerland, utility calculations based on the German or French value set would be an obvious choice. Our results suggest that the German value set may not be the most appropriate for use with Swiss cancer patients. The French and EU value sets may be relevant alternatives and improve international comparability.