Background: The EQ-5D is one of the most recommended questionnaires for cost-effectiveness studies.
Aims: To study the psychometric properties of the EQ-5D-5L in patients with major depression.
Methods: This prospective observational study included 433 patients with major depression who completed the EQ-5D-5L and Patient Health Questionnaire-9 (PHQ-9) questionnaires at baseline, of whom 310 also did six months later. The structural validity was assessed by confirmatory factor analysis, the item functioning by item response analysis, and reliability by Cronbach's alpha. Convergent validity and known-groups validity was studied using the PHQ-9 and a general health question. To assess responsiveness effect sizes were calculated.
Results: The results supported the unidimensionality and showed adequate item functioning, with somewhat age-related item differential functioning for the mobility dimension. Cronbach's alpha was 0.77. The EQ-5D-5L showed a high correlation with the PHQ-9 and general health. The more severe the depression level and the poorer the general health, the lower the EQ-5D-5L scores (p < 0.001). Responsiveness parameters showed moderate changes among "improved" patients.
Conclusions: These findings support the adequate psychometric properties of the EQ-5D-5L in patients with major depression. It could be very useful for clinicians and researchers as an outcome measure and for use in economic evaluation.
Keywords: EQ-5D-5L; depression; economic evaluation; item response theory; psychometric properties; utility index.