Comparison and concordance of health-related quality of life tests among substance users

In the field of drug and alcohol abuse, health-related quality of life (HRQoL) has been used as an important clinical and research outcome. The aim of this study was to establish score linkages (concordance) among three HRQoL assessment tools: WHOQOL-BREF, DUQOL and HRQOLDA scores, applying a Rasch-based common person equating procedure. One hundred and twenty one adults were recruited from inpatient and outpatient treatment facilities in Sydney West Area Health Service. WHOQOL-BREF, DUQOL and HRQOLDA tests were administered. Item parameters were calculated applying Rating Scale Model, a Rasch model. Fit statistics suggest acceptable goodness-of-fit to the RSM for three instruments. Correlations between HRQOLDA and WHOQOL-BREF and between HRQOLDA and DUQOL scores were 0.719 and 0.613, and the RiU index was 30.4 % and 20.9 %, respectively. All three tests performed adequately for differentiating between individuals whose scores are located at different points along the continuum of the HRQoL construct. The results demonstrated a higher concordance between the HRQoLDA and WHOQOL-BREF than between the HRQoLDA and the DUQOL. However, it cannot be established unequivocally that the scores of these tools are concordant. In this study, the utility of the application of the Rasch model to provide an empirical benchmark for the selection of measurement tools to be used in the context of health care and research is demonstrated.