Development and Use of Cognition Bolt-Ons for the EQ-5D-3L and EQ-5D-5L: A Systematic Review

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 3 electronic databases, following Preferred Reporting Items for Systematic Reviews and Meta-Analysis 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 (3-level: 23, 5-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 proxy reporting. 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. Conclusions 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 standardized cognition bolt-on item(s) for relevant contexts.