Quantification of the level descriptors for the standard EQ-5D three-level system and a five-level version according...

Area of Science:

• Health Economics
• Psychometrics
• Outcome Measurement

Background:

• The EQ-5D is a widely used patient-reported outcome measure.
• The standard three-level (3L) system has limitations in capturing health state nuances.
• A five-level (5L) version has been developed to enhance descriptive power.

Purpose of the Study:

• To quantitatively compare the level descriptors of the EQ-5D 3L and 5L systems.
• To evaluate the equidistance, isoformity, and consistency of level descriptors.
• To assess the performance of direct and vignette-based indirect measurement methods.

Main Methods:

• Eighty-two respondents rated non-extreme level descriptors using a visual analog scale (VAS).
• Respondents scored 15 health scenarios using 3L, 5L, and VAS scales.
• Investigated equidistance, isoformity, and cross-dimensional consistency of level descriptors.

Main Results:

• Equidistance was rejected for both 3L and 5L without transformation, but satisfied for 5L after transformation.
• Isoformity results were mixed, indicating some differences between identical level descriptors across systems.
• Consistency between dimensions was satisfied for both instruments and methods.

Conclusions:

• Level descriptors exhibit similar distributions within each system but differ between the 3L and 5L versions.
• The study provides evidence for the enhanced descriptive power of the 5L EQ-5D.
• Findings support the continued development of an official five-level EQ-5D system.