EQ-5D Bolt-on Toolbox

Summary

• EQ-5D Bolt-on^TM: A bolt-on dimension is a supplementary item, or set of items, that extend the measurement scope of the EQ-5D beyond its core dimensions, addressing specific health-related quality of life dimensions that the original instrument does not fully capture.
• EQ-5D Bolt-on Toolbox^TM: A curated collection of EQ-5D Bolt-ons to be used in combination with EQ-5D-5L in specific, well-defined circumstances.
• Applicability: Bolt-ons must be used alongside EQ-5D-5L; they are not standalone measures.
• Current bolt-ons in development: The EQ-5D Bolt-on Toolbox includes generic (cognition, fatigue, sleep), functioning- (hearing, vision) and symptom-specific (breathing problems, skin) bolt-ons. Note that the bolt-on names are working titles.
• Availability: Currently the EQ-5D Bolt-on Toolbox has experimental status and is accessible to collaborators (including commercial users) upon registration and signing a collaborator agreement.
• Use guidelines: The addition of a bolt-on does not affect standard analysis of EQ-5D-5L data. Bolt-ons provide supplementary information.
• Timelines: The launch of the EQ-5D Bolt-on Toolbox as an approved version is expected in Q4 2028, with multiple languages and modes of administration (self-complete, proxy 1, interviewer-administered).

Detailed Description

Rationale for the EQ-5D Bolt-on Toolbox
EuroQol is committed to continuously improving its instruments and keeping them relevant as the field of health outcomes measurement evolves. The EQ-5D is the shortest generic preference-weighted measure of health-related quality of life, consisting of five single-item dimensions. Over the past 30 years it has become the most commonly used generic preference-weighted measure of health-related quality of life. It is a valid, reliable and responsive instrument across most disease groups, populations, health interventions and contexts. However, with thousands of diseases affecting different aspects of health-related quality of life, it is unrealistic to expect that the five single-item dimensions in the EQ-5D-5L will fully cover all aspects of all conditions. In certain populations, adding a targeted health-related quality of life dimension may enhance the measurement scope of the EQ-5D-5L. The EQ-5D Bolt-on Toolbox does this, and aims to address user needs in both health technology assessment and non-health technology assessment contexts.

EQ-5D Bolt-on Toolbox^TM
The EQ-5D Bolt-on Toolbox aims to complement the EQ-5D-5L in specific, well-defined circumstances. Currently it is in development and has experimental status. It includes a carefully chosen set of bolt-ons addressing specific health-related quality of life dimensions in clinical populations where a clear need has been demonstrated, whether based on psychometric evidence or valuation, allowing users to expand the measurement scope of EQ-5D in certain populations. Each bolt-on in the Toolbox will be selected, developed, validated and, where relevant, valued in accordance with EuroQol protocols and standards.

Scope and types of bolt-ons
The EQ-5D Bolt-on Toolbox will include bolt-ons only for health-related quality of life dimensions and not beyond. The Toolbox will include bolt-ons only for the EQ-5D-5L, not for the EQ-5D-3L. It will be flexible, allowing for the gradual expansion of the number of bolt-ons as development progresses. The Toolbox will include both generic bolt-ons as well as those targeting specific functioning or symptoms. At this point, EuroQol does not intend to include condition-specific bolt-ons – those designed to capture aspects of health-related quality of life relevant to a particular condition.

Development process
The EQ-5D Bolt-on Toolbox currently has an experimental status and is therefore only available to research collaborators upon signing a collaboration agreement. Any user, whether commercial or non-commercial, can apply to become a research collaborator. The bolt-ons within the Toolbox are being developed to a high standard in accordance with strict EuroQol guidelines, using both qualitative and quantitative methods to ensure that they are acceptable to patients and demonstrate strong measurement characteristics. Involvement of the affected groups targeted by each bolt-on is essential to ensure their relevance to those directly impacted. This process ensures that the bolt-ons from the EQ-5D Bolt-on Toolbox are fit for purpose.

Which bolt-ons are available?
The following bolt-ons are available in the Experimental version of the EQ-5D Bolt-on Toolbox: breathing problems, cognition, fatigue, hearing, skin, sleep and vision. Please note that the names of the bolt-ons are working titles referring to the areas of health-related quality of life they measure, as they are still under development, and may not reflect the final item naming. EuroQol may consider developing and adding further bolt-ons to the Toolbox in the future; however, for now, development efforts are focused those listed above.

Applications
Bolt-ons have been extensively researched in a variety of settings, including observational studies, routine outcome measurement, clinical trials, economic evaluations and the assessment of disease burden. They are expected to be especially valuable in certain patient populations to complement the EQ-5D-5L and offer a deeper and more nuanced assessment at health-related quality of life. What makes bolt-ons particularly useful is their ability to expand the EQ-5D-5L’s measurement scope, while maintaining its familiar structure, format and recall period. This means that users can get a more comprehensive health-related quality of life assessment without having to turn to other instruments. Importantly, the development of the Toolbox means that the EQ-5D-5L remains a valid standard instrument, with the Toolbox offering an option to enhance sensitivity in targeted dimensions of health-related quality of life. Bolt-ons can only be used as part of registered studies that include the EQ-5D-5L; they are not intended for use as standalone measures. Users can analyse EQ-5D-5L data as usual, while also reporting the additional descriptive information provided by the bolt-on.

Value sets
EuroQol is currently undertaking methodological research on methods for valuation of the bolt-ons in the Toolbox. EuroQol will only endorse value sets that are developed in line with this protocol for bolt-ons within the Toolbox. As a bolt-on may be used not only in health technology assessment contexts but also in applications with a different purpose than estimating quality-adjusted life years (e.g. observational studies, routine outcomes measurement), not all bolt-ons will necessarily have associated value sets. However, even without value sets, bolt-ons can still play an important role in providing a more comprehensive picture of health-related quality of life across different populations. Until the first value sets become available, appropriate descriptive analyses will be recommended.

Distribution
EuroQol aims to distribute the EQ-5D Bolt-ons that are included in the Toolbox through the registration page, along with guidance for their application, ensuring consistent and effective use in health-related quality of life measurement. Bolt-ons not included in the Toolbox are not recommended to be used. The launch of the Approved Bolt-on Toolbox is expected to be in Q4 of 2028.

Available languages
Once launched, bolt-ons in the EQ-5D Bolt-on Toolbox will be made available in multiple languages similarly to other EuroQol instruments. If you would like to enquire about a language version or initiate a new researcher-led translation, please contact EuroQol at the email addresses below.

Available versions
For the Approved Bolt-on Toolbox, self-complete, proxy 1 and interviewer-administered versions will be created for all bolt-ons.

Decision-making on bolt-ons included in the EQ-5D Bolt-on Toolbox
Decisions on the inclusion of specific bolt-ons in the Toolbox will be made by EuroQol, leveraging its expertise in health measurement and valuation, alongside its role as the owner of the intellectual property and steward of the EQ-5D’s integrity and applicability.

Ongoing research with the bolt-ons
Bolt-ons are being developed and tested in multiple ongoing EuroQol-funded projects, involving diverse patient populations and the general public across over 10 countries. Furthermore, ongoing research projects are focused on developing appropriate valuation methods for bolt-ons.

Interested in developing and testing bolt-ons?
EuroQol supports innovation and the expansion of health-related quality of life measurement tools through collaboration with researchers. If you are interested in contributing to the development, testing and valuation of bolt-ons, we encourage you to engage with us early in the process. This ensures alignment with the EQ-5D framework and allows you to benefit from EuroQol’s expertise and guidance.

Contact Details:

Fanni Rencz – Programme Director: rencz@euroqol.org
Brendan Mulhern – DSWG chair: brendan.mulhern@uts.edu.au