Crosswalk algorithms for the conversion of mean EQ-5D indices calculated with different value sets.

Abstract

The EQ-5D questionnaire of EuroQol is an important tool, not only for researchers, but also for quality registers. Until 2013, Sweden did not have a country-specific value set to convert the EQ-5D health states into a single index. Commonly, the UK time trade-off (UK TTO) value set has been used. The study reported here aimed to establish an easy to use tool for the bidirectional crosswalk of the mean EQ-5D values based on two different value sets: the UK TTO and the Swedish TTO value sets. Using an artificial data set encompassing all possible EQ-5D outcomes, we calculated the EQ-5D index using both the UK TTO and Swedish TTO value sets. Thereafter we modelled the relationship between the two indices using least-squares regression and major axis regression. A series of simulations was run to assess the feasibility of the obtained crosswalk algorithms. Major axis regression was superior to ordinary least-squares regression. Converting the mean EQ-5D values from the UK TTO scale to the Swedish TTO scale was more accurate than the inverse conversion. Values close to the floor and ceiling of the EQ-5D index were more challenging to crosswalk. CONCLUSIONS WE ESTABLISHED ALGORITHMS BASED ON MAJOR AXIS REGRESSION TO CROSSWALK EQ-5D VALUES BASED ON THE UK TTO AND THE SWEDISH TTO VALUE SETS THE PRESENTED ALGORITHM MAY FACILITATE COMPARISONS OF EQ-5D VALUES WHEN ONLY MEAN VALUES ARE AVAILABLE THE EXISTENCE OF A CROSSWALK ALGORITHM WILL EASE THE TRANSITION FROM THE UK TTO TO THE SWEDISH TTO VALUE SET.