This study aimed to map the World Health Organization Quality of Life–BREF (WHOQOL-BREF) onto the 5-level EQ-5D (EQ-5D-5L) using a real Thai valuation set of the EQ-5D-5L. The second objective was to explore the impacts of the differences between observed and predicted EQ-5D-5L index scores on the incremental cost-utility ratio (ICUR) using 5 hypothetical scenarios.
This is a secondary data analysis. A total of 800 outpatients with chronic diseases were recruited from 2 university hospitals in Bangkok, Thailand, between July 2014 and March 2015. The 800 patients were randomly divided into 2 samples: estimation and validation samples. The estimation sample was used to assess the relationships between the EQ-5D-5L index score and 4 WHOQOL-BREF dimension scores and to find the best-fit model and its equation. For the validation sample, the equation of the best-fit model from the estimation sample was used to calculate predicted EQ-5D-5L index scores.
A multiple linear regression showed that only the physical domain of the WHOQOL-BREF was significantly associated with the EQ-5D-5L. Among 11 regression models, the curve estimation found that the inverse model was the best-fit model. The prediction equation of EQ-5D-5L was equal to 1.385 minus 7.572/physical domain of the WHOQOL-BREF. The impacts of the differences between the observed and predicted EQ-5D-5L index scores on ICUR were only 0.4% to 1.8% from the base case.
A nonlinear relationship between the physical domain of the WHOQOL-BREF and EQ-5D-5L utility was shown. The impacts of the differences between the observed and predicted EQ-5D-5L index scores on ICUR were minimal.