Interchangeability of the EQ-5D and the SF-6D, and comparison of their psychometric properties in a spinal postoperative Spanish population.

Objective: EuroQol-5D (EQ-5D) and Short-Form Six-Dimensions (SF-6D) are widely used to calculate quality-adjusted life-years in cost-utility analysis. The choice of the instrument could influence the results of cost-utility analysis. Our objective was to compare the psychometric properties of the EQ-5D and SF-6D in a postoperative Spanish population, as well as assess their interchangeability in a cost-utility analysis.

Methods: Ambispective study. Methods: Tertiary public hospital. Methods: 275 Spanish patients who had undergone surgery for lumbar disc herniation. Methods: Patients completed EQ-5D-3L and Short-Form 36 (SF-36v2) questionnaires. Internal consistency, floor and ceiling effects, agreement, and construct validity (convergent validity, including dimension-to-dimension correlations, and "known groups" validity) were assessed. The Spanish tariffs were applied. Methods: Cronbach's α coefficient, Spearman's rank correlation coefficient, Lin's concordance correlation coefficient, intraclass correlation coefficient and Bland-Altman plot.

Results: Main findings were: (a) lack of agreement between EQ-5D and SF-6D utilities (Lin's concordance correlation coefficient: 0.664 [95% CI: 0.600-0.720]; the Bland-Altman plot showed a mean difference of 0.0835 and wide limits of agreement [- 0.2602-0.4272]). (b) Lack of correlation between domains that theoretically measure similar aspects of quality of life, with the exception of "pain" domain.

Conclusions: The preference-based EQ-5D and SF-6D instruments showed valid psychometric properties to assess generic outcome in a Spanish population who had undergone surgery for lumbar disc herniation; however, utility scores derived from the measures were different. Thus, these two instruments cannot be used interchangeably to perform a cost-utility analysis, and they should both be included in sensitivity analyses.