To compare the utility values and quality-adjusted life years (QALYs) obtained by the Time Trade-Off instrument (TTO) and the EuroQol-5D (EQ-5D) in patients with rheumatoid arthritis (RA); to analyze the association between utility values and Disease Activity Score 28 (DAS28) and Health Assessment Questionnaire (HAQ).
We conducted a longitudinal, prospective, 1-year study of RA patients selected randomly from 10 rheumatology clinics. TTO and EQ-5D were administered at 4 scheduled visits.
The study sample comprised 300 RA patients (82% women, mean age 59 years, mean disease duration 10.3 years). A total of 260 patients completed both the TTO and the EQ-5D at baseline, and the mean +/- SD TTO scores were significantly higher than the EQ-5D scores (0.81 +/- 0.22 versus 0.53 +/- 0.35, P < 0.0001). The intraclass correlation coefficient (ICC) for the utility methods was 0.19. Data about changes in both TTO and EQ-5D scores during the study year were available in 163 patients. These changes tended to be larger in the TTO scores than the EQ-5D scores (mean +/- SD 0.05 +/- 0.25 versus -0.005 +/- 0.35, P = 0.054). The ICC for the mean changes in the utility scores was 0.24. Patients obtained a mean +/- SD of 0.04 +/- 0.20 QALYs based on TTO scores and 0.004 +/- 0.27 based on EQ-5D scores (P = 0.12). At baseline, the EQ-5D scores were highly correlated with the HAQ (r = -0.74) and moderately correlated with the DAS28 (r = -0.47), whereas the TTO correlated poorly with both the HAQ and DAS28. Correlation between the mean change in the EQ-5D and in the HAQ was moderate (r = -0.55).
TTO and EQ-5D do not yield the same utility values. The results suggest that the EQ-5D is more representative of RA status than the TTO, a valuable conclusion when addressing economic evaluations in RA.