Development and use of cognition bolt-ons for the EQ-5D-3L and EQ-5D-5L : a systematic review

Abstract

Objectives: Multiple studies have proposed adding a cognition dimension (bolt-on) to the EQ-5D. Our objective was to systematically review the existing literature on the development and use of cognition bolt-ons for the EQ-5D. Methods: A systematic literature review was conducted to identify studies that developed or used a cognition bolt-on for EQ-5D-3L or EQ-5D-5L (PROSPERO: CRD42023445567). We searched in three electronic databases, following PRISMA 2020 guidelines. The methodological quality of bolt-on items was assessed using criteria adapted from Mulhern et al. 2022. Results: From 1997 to 2023, 181 publications (covering 137 studies) were included showing an increasing use of cognition bolt-ons over time. We identified 52 distinct wordings (three-level: 23, five-level: 29), with the most common dimension titles being cognition (29%) and thinking ability (19%), and examples such as concentration (60%), memory (39%) and remembering (31%). The methodological quality of bolt-on development was heterogeneous, often lacking qualitative input in item wording or clear phrasing. Bolt-ons were used in 28 languages across 24 countries, with 64% of the studies originating from the Netherlands. Overall, 16% of the studies used proxyreporting. Most studies developed (n=38) and used or psychometrically tested EQ-5D+bolt-on(s) (n=120), with fewer valuation and disability weight studies (n=27). These studies covered 71 patient populations, most commonly injuries, dementia, depression, HIV, schistosomiasis and stroke. Conclusion: There is a growing demand for cognition bolt-ons across various medical specialties. The variation in cognition bolt-on items poses challenges for comparability and consistent healthcare decision-making. Our findings will guide research toward selecting standardised cognition bolt-on item(s) for relevant contexts.