The remarkably frequent use of EQ-5D in non-economic research.

EQ-5D is an instrument which has been utilized for a variety of purposes, including in health-economic appraisals as an input into quality-adjusted life year (QALY) calculations. Indeed, it is the most-widely applied instrument for health-economic appraisal worldwide, and is recommended for use in QALY calculations by many national Health Technology Assessment (HTA) agencies. There is also a growing body of evidence for its usefulness in a variety of settings other than economic appraisals, but such use has not been well-documented. This study addresses this issue and documents how EQ-5D has been applied in both the non-economic and economic contexts. The PubMed database was searched using the terms 'EQ-5D', 'EQ-5D AND cost', and 'EQ-5D AND cost AND QALY' from 1 January 1980 to 31 December 2019. We concentrated on 2019 publications for more detailed analyses. All the data collected for 2019 were downloaded and collected in EndNote. For 2019 only, we classified economic and non-economic use based on the inclusion of 'cost'. We also checked by manual inspection whether the search terms were suitable in correctly identifying economic and non-economic use. Variants of the non-economic use of EQ-5D were classified as follows: (a) as a quality of life outcome measure; (b) as a tool for methodological research; (c) methodological issues of EQ-5D itself; (d) comparisons with other quality of life questionnaires; (e) mapping studies; (f) value sets; (g) alongside costs but no QALY calculated; and (h) other. The first publication found was from 1990. Up to and including 2019, 10,817 publications were identified, of which more than two in three did not contain any reference to costs or QALYs. In 2019, a total of 1409 manuscripts were identified, of which 239 were specifically for EQ-5D-5L.  Four hundred and seven (28.9%) included some form of 'costs' and 157 (11.1%) both 'costs' AND 'QALYs' terms. For EQ-5D-5L, the corresponding numbers were 104 (43.5%) and 29 (12.1%), respectively. After manually checking all the 1409 papers, three were duplicated records, which were omitted. In the remaining 1406 papers, only 40 (2.8%) contained the term 'cost', but not 'cost per QALY', and only 117 (8.3%) were identifiable as economic evaluations using the term 'cost per QALY'. Most non-economic use of EQ-5D was as a quality-of-life outcome measure (72.8%). Other applications were: as a tool for methodological research (6.7%); comparison studies (3.7%); EQ-5D methodological issues (3.5%); containing costs but not QALYs (2.8%); mapping (1.3%); value sets (0.4%); and other papers (0.4%). The majority of the studies retrieved, covering a wide variety of research areas, reported upon the non-economic use of EQ-5D. Despite being the most-used instrument worldwide for QALY calculations, economic appraisal accounted for only a small, but important, part of published use.

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