Objectives: To test the psychometric properties of the EUROHIS-QOL 8-item index, a shortened version of the World Health Organization Quality of Life Instrument-Abbreviated Version (WHOQOL-BREF).
Methods: The sample consisted of 2359 subjects identified from primary care settings, with 1193 having a confirmed diagnosis of depression. Data came from six countries (Australia, Brazil, Israel, Russia, Spain, and the United States) involved in a large international study, the Longitudinal Investigation of Depression Outcomes. The structure of the EUROHIS-QOL 8-item index follows that of the WHOQOL-BREF assessment. Internal consistency was measured by using Cronbach's alpha. Convergent validity was assessed by using correlations with different measures for mental health (Symptom Checklist 90), physical health (self-evaluation), and quality of life (WHOQOL-BREF and short form 36 health survey). Discriminant group validity was assessed between diagnosed depressed and nondepressed patients. Differential item functioning and unidimensionality were analyzed by using Rasch analysis. Factor structure was assessed with structural equation modeling analyses.
Results: Internal consistency was acceptable (ranged between 0.72 and 0.81 across countries), and the index discriminated well between depression (t = 6.31-20.33; P < 0.001) across all countries. Correlations between the EUROHIS-QOL 8-item index and different measures--Symptom Checklist 90 (r = -0.42), physical health (r = -0.42), WHOQOL-BREF domains (r = 0.61-0.77), and short form 36 health survey (r = 0.58)--were all significant (P < 0.001). The index is unidimensional with desired item fit statistics. Two items ("daily living activities" and "enough money to meet your needs") had residuals exceeding 4. Differential item functioning was observed with general quality of life, general health, relationships, and home items for age. A common one-factor structure with acceptable fit was identified in three out of six countries (comparative fit index = 0.85, root mean square error of approximation = 0.11).
Conclusions: The EUROHIS-QOL 8-item index showed acceptable cross-cultural performance and a satisfactory discriminant validity and would be a useful measure to include in studies to assess treatment effectiveness.
Copyright © 2012 International Society for Pharmacoeconomics and Outcomes Research (ISPOR). Published by Elsevier Inc. All rights reserved.