Introduction: The EQ-5D provides preference weights (utilities) for health-related quality of life to be used for calculating quality-adjusted life years (QALYs) in cost-utility analysis. The aim of this study was to compare differences in EQ-5D utility scores with differences in quality of life, psychopathology, and social functioning scores.
Methods: In an observational longitudinal cohort study, EQ-5D utilities (EQ visual analogue scale (EQ VAS), EQ-5D indices of the United Kingdom (EQ-5D index-UK) and Germany (EQ-5D index-D)) were compared with scores of the WHOQOL-BREF, CGI, and GAF at baseline and at 18 months (N=104). The patients' health status at follow-up was categorized as "worse", "stable", or "better" using the EQ-5D transition question (patient-based anchor) and the Bech-Rafaelsen melancholy scale (clinician-based anchor). Effect sizes (ES) were used to compare differences in scores within each group over time; regression analysis was used to derive meaningful difference scores in health status associated with a shift from "stable" to "better" health status.
Results: The most responsive instrument was the CGI (patient-based anchor: ES=|0.98|; clinician-based anchor: ES=|1.35|); responsiveness was large in EQ VAS (patient-based anchor: ES=|0.84|; clinician-based anchor: ES=|1.19|), but rather small to medium for EQ-5D index-UK (patient-based anchor: ES=|0.55|; clinician-based anchor: ES=|0.65|) and EQ-5D index-D (patient-based anchor: ES=|0.41|; clinician-based anchor: ES=|0.45|). Compared with the other instruments, the shift to a "better health status" was smaller if elicited by the EQ-5D indices.
Discussion: Both EQ-5D indices were less responsive and need larger patient samples to detect meaningful differences compared with EQ VAS and the other instruments.