Sleep and fatigue/energy bolt-ons for the EQ-5D-3L and EQ-5D-5L: a systematic review

This study systematically reviewed the development, use, psychometrics, and valuation of sleep and fatigue/energy bolt-ons for the EQ-5D-3L and EQ-5D-5L.

A systematic review was conducted based on key elements of the PRISMA 2020 guidelines. Searches on PubMed, Embase, and Web of Science, supplemented by citation tracking and manual Google Scholar and EuroQol conference searches, were used. Key study characteristics, bolt-on specifications, psychometric properties, and valuation evidence were summarized narratively.

Twenty-one publications from 19 unique studies conducted in 19 countries were published between 1991 and 2025. Sleep and fatigue/energy bolt-ons were used together in 13 studies. Twelve distinct sleep and 14 fatigue/energy bolt-on versions have been developed, mostly in five-level formats (sleep=67%; fatigue/energy=71%). The development of 3 sleep and 5 fatigue/energy bolt-ons was supported by qualitative evidence. Quantitative evidence from 13 sleep and 13 fatigue/energy bolt-on studies revealed bolt-ons commonly reduced ceiling effects although not across all conditions (absolute reduction: sleep=0.3-30.0%, fatigue/energy=1.9-30.9%), showed good convergent validity with conceptually related external measures or their items/domains, and improved EQ VAS explanatory power (sleep=0.7-10.0%, fatigue/energy=0.1%-3.7%). Findings on known-group validity were heterogeneous across clinically relevant known-groups. Evidence on test-retest reliability (n=1) and responsiveness (n=3) was limited. Valuation evidence (n=5) regarding the impact of bolt-ons on preferences was scarce and inconclusive.

The development of sleep and fatigue/energy bolt-ons to date has lacked sufficient qualitative input, while some psychometric findings supported their added value to the EQ-5D. Future mixed-methods bolt-on development and refinement studies are needed for both constructs.