Abstract
The EQ-5D is one of the most widely used generic preference-weighted measures of health-related quality of life (HRQoL), and is recommended by health technology assessment agencies worldwide. The EQ-5D is a valid, reliable and responsive measure for the majority of populations, interventions and contexts. However, in some specific patient populations, important aspects of HRQoL may not be fully captured by its five dimensions, which may limit content validity and responsiveness to changes in HRQoL. To address these specific gaps, the EQ-5D Bolt-on Toolbox™ is being developed to provide a set of additional dimensions (bolt-ons) for use alongside the EQ-5D-5L in specific patient populations. This article (i) explains the rationale, history and objective for the bolt-on approach and the EQ-5D Bolt-on Toolbox; (ii) presents the selection process for dimensions proposed for inclusion in the EQ-5D Bolt-on Toolbox; (iii) describes its current status and management framework; (iv) outlines the development process; (v) describes approaches to reporting data; vi) discusses valuation options and plans; and (vii) outlines potential applications and future directions. The Toolbox currently has ‘experimental status’, indicating that it is in development. The Toolbox development is following a standardised framework incorporating qualitative and quantitative psychometric methods and exploring various valuation approaches. Current development focuses on eight candidate bolt-ons (breathing problems, cognition, fatigue, hearing, self-confidence, skin irritation, sleep and vision). Bolt-ons were selected based on evidence demonstrating their ability to address HRQoL gaps not captured by the EQ-5D-5L in certain patient populations, prioritising symptoms, functioning and health impacts that are applicable across multiple diseases and settings. Guidance will be developed on the reporting of data collected using bolt-ons, and separately for the valuation and appropriate use of bolt-ons. Users can continue to analyse and report EQ-5D-5L data as usual, maintaining comparability, while also benefiting from the supplementary information provided by the bolt-on(s). The Toolbox is intended for both economic and non-economic applications (e.g. routine outcomes measurement).