Evaluation of the SF-36 Health Index Applied to Methadone Maintenance Program Users. Reference Values for the Basque Autonomous Community, Spain

Abstract

Background: The questionnaires that measure perceived health are used in clinical practice to determine the impact of illnesses and the benefits of treatments. Population-based norms have been proposed to increase their interpretability. The aim of this paper was to obtain reference values for users of Methadone Maintenance Programs (MMP) in the Basque Autonomous Community (BAC). Methods: Cross-sectional study carried out in 2000 on a stratified random sample of users included in MMP of BAC (n= 726). SF- 36 Health Survey was used; central trend, dispersion and percentile data were estimated for each of the SF-36 dimension scores to generate reference values according the dwell time in the methadone program. Results: All Cronbach s alpha coefficients were higher than 0.7, and the percentage or non-responds were lower 1%. The MMP users had lower punctuations in all dimensions of SF-36 that population values of reference (p < 0.001). The health status of the participants was worse among those than they began the treatment that among those that took more than six months in the MMP; the differences in all SF-36 dimensions scores were statistically significant (p < 0.001). Conclusions: The SF-36 as a measure of health status in MMP population shows a high internal consistence, and is able to discriminate patients with different stages of treatment evolution. Results presented should be considered the population-based norms for monitoring the improvement progression or response to treatment in patients included in MMP.