Estimating the relationship between EQ-5D-5L and EQ-5D-3L: results from an English population study

There are two versions of the EQ-5D for measuring and valuing health in adults in the UK. The descriptive system for both comprises a classification that allows respondents to indicate their health state on five dimensions of health: mobility, ability to self-care, ability to undertake usual activities, pain and discomfort, and anxiety and depression. In the EQ-5D-3L version (3L from here), respondents indicate the degree of impairment on each dimension according to three levels (no problems, some problems, extreme problems). The three-level version of EQ-5D (3L) is the most widely used preference based measure in economic evaluations across the National Institute for Health and Care Excellence’s (NICE’s) guideline producing programmes. It is currently explicitly recommended for reference case analyses in the Guide to the Methods of Technology Appraisal (Section 5.3).1

A newer, five-level version of the instrument has been developed. EQ-5D-5L (5L from this point) includes five levels of severity for each dimension (no problems, slight problems, moderate problems, severe problems, and extreme problems). There is no currently approved value set for the 5L in England. However, the 5L descriptive system is increasingly used in clinical studies. Therefore, there is a requirement to estimate health state utility values for the 5L system based on the 3L value set via “mapping”.

We know that 3L and 5L cannot be treated as if they were equivalent2 3. Therefore, some means of linking from responses individuals give to the 5L to the responses we would have seen had they filled in the 3L and the associated values currently needs to be used. In future, the ability to link from older 3L evidence to 5L will be required, should an acceptable 5L value set for England be produced.

Van Hout et al4 provide an option for mapping, which we refer to henceforth as the “Crosswalk”. It is the approach recommended in the NICE 2013 Methods Guide. Van Hout et al estimate 3L from 5L responses using a series of modified cross-tabulations of responses to the 3L and 5L instruments, for each dimension of health separately. The approach is based on data provided by the EuroQol Group (EQG).

Alternative mappings have been derived from a modelling approach developed by Hernández Alava and Pudney5 for the NICE Decision Support Unit (DSU), using a multi-equation statistical model of the joint 3L and 5L responses. Originally estimated using a sample of patients with rheumatoid arthritis from FORWARD, the National Data Bank for Rheumatic Diseases, the model was subsequently re-estimated using the same EQG dataset as van Hout et al. (see Wailoo et al6). Results from the model have been made available to cost effectiveness analysts through pre-programmed commands for popular software including Stata, R and Excel. Comparisons between both the methods and results of the Crosswalk and DSU approaches were reported in an earlier DSU report.7

We now report on an updated analysis for mapping from 5L to 3L, using the same methods developed by Hernández Alava and Pudney for the DSU but based on a new dataset. It is important to note that these methods treat the 3L and 5L responses symmetrically and therefore provide the added functionality of mapping from 3L to 5L, which may be an important future option should a suitable 5L value set be developed for use in England. The approach has the advantage that mappings from 3L to 5L and 5L to 3L are logically consistent, which will not generally be true if separately-derived 3L5L and 5L3L mappings are used.8