Expansion of the EQ-5D health state classifier to 5 levels (EQ-5D-5L) has been proposed to improve discriminative and evaluative properties, but current preference-based algorithms were developed for a 3-level (EQ-5D-3L) structure. The objectives were to examine equivalency of meaning between 3L and 5L response systems, and to psychometrically derive a system of weights that facilitate conversion of 3L preference-based algorithms to a 5L system.
Rasch models were used to examine the equivalency of the 3L and 5L systems using 2 datasets where health status was assessed using the 3L and 5L: a Dutch study of primarily hypothetical health state assessments and a US-based multicenter study of 423 cancer patients. Category-specific mean values of latent person parameters (using maximum likelihood estimation) for the levels of the 3L and 5L systems were estimated.
Means on the latent continuum pertaining to level 3 in the 5L system and level 2 in the 3L (some problems) were similar for both datasets, suggesting equivalence of these levels. Extremes of the 5L response structure consistently broadened the measurement continuum. By anchoring “no problems” as 0 disutility, disutility weights from EQ-5D-3L were transformed into weights for EQ-5D-5L using ratios of logit distances between person means for 5L and 3L calibrated for each dimension using the Rasch model.
This study illustrates the rich potential for modern psychometric techniques both to examine equivalency when health status measures are modified as well as to inform preference-based measurement systems using existing value sets.
From the *Department of Pharmacy Practice, Center for Pharmacoeconomic Research, College of Pharmacy, University of Illinois at Chicago; †Center for Management of Complex Chronic Care, Hines VA Hospital, Hines, Illinois; ‡Institute for Community Medicine, University of Greifswald, Greifswald, Germany; §Department of Epidemiology, Academic Medical Center, Amsterdam, Netherlands; and ¶Department of Psychiatry and Behavioral Sciences, Center on Outcomes, Research and Education, Evanston Northwestern Healthcare, Northwestern University Feinberg School of Medicine, Evanston, Illinois.
The authors are grateful for partial funding support from the EuroQol group. The original data collection that focused on the validation of symptom assessment scales in cancer was supported by a consortium of 10 pharmaceutical companies.
This work was accepted for podium presentation at the annual ISOQOL conference in Lisbon Portugal, Oct 14–16, 2006 and an earlier version of the article may appear in the proceedings of the 24th Scientific Plenary of the EuroQol Group.
The views expressed in this article are the solely those of the authors and do not necessarily represent the views of the EuroQol Group. The 5L versions of the EQ-5D were experimental prototypes and are not officially recognized by the EuroQol Group.
Reprints: A. Simon Pickard, PhD, Center for Pharmacoeconomic Research, College of Pharmacy, University of Illinois at Chicago, Rm 164, MC 886, 833 South Wood Street, Chicago, IL 60612. E-mail: firstname.lastname@example.org.