[Injection Drug User Quality of Life scale (IDUQoL): psychometric assessment of the Spanish version].

BACKGROUND: The assessment of quality of life has become one of the priority indicators of outcomes in the field of clinical research. Therefore, it is necessary to use instruments adapted to and validated for the context in which they are to be used.
PURPOSE: To assess the psychometric properties of the IDUQoL (Injection Drug User Quality of Life Scale) in its Spanish adaptation.
METHOD: Participants were 100 persons with a diagnosis of opiate addiction who were on a methadone maintenance programme. They responded to the IDUQoL -in its 21-domain version- and two other quality of life instruments (the SF-36 and the EQ-5D).
RESULTS: Good reliability data are obtained (Cronbach's alpha of 0.92 and Intraclass Correlation Coefficient for the test-retest of 0.79). Exploratory and confirmatory factor analyses and semi-partial correlations analysis confirm the unidimensionality of the construct, with explained variance of 43.8% and adequate fit indices (GFI = 0.92; CFI = 0.97; RMSEA = 0.044). Convergent and criterion-related validity were also quite adequate (correlation coefficients with the SF-36 and EQ-5D were situated between 0.34 and 0.61, and with other criterion variables between 0.23 and 0.39; p <0.05), even though the discriminant validity analysis is not completely conclusive.
CONCLUSION: The findings from this study provide evidence to support the use of the IDUQoL as a specific quality of life instrument in the addictive disorders context, and confirm its appropriate characteristics in the Spanish adaptation.