Measuring utilities by the time trade-off method in Tunisian rheumatoid arthritis patients

The objective of this study was to determine the feasibility, reliability and validity of the time trade-off (TTO) in Tunisian rheumatoid arthritis (RA) patients. The TTO was used to measure the utility in 122 RA patients with increasing difficulty in performing activities of daily living. The 1-week test-retest reproducibility was studied in 57 patients using the intraclass correlation coefficient (ICC). Validity was evaluated by comparison with other outcome measures: utility rating scale (RS), quality of life (QOL) [arthritis impact measurement scale 2 (AIMS2), rheumatoid arthritis quality of life (RAQOL)], functional status [health assessment questionnaire (HAQ), Lee index] and disease activity score (DAS). Eight patients (6.6%) did not complete the TTO. The median value of the TTO score was 0.655 (0.019-1.000). The ICC for reliability of the TTO was 0.89 (p<0.001). The TTO showed poor to moderate correlation (Spearman's correlation coefficients between 0.2 and 0.409, p<0.01) with AIMS2, RAQOL, HAQ and Lee index. We did not find any correlation between TTO and DAS. Multiple regression analysis showed that only 32% of TTO scores could be explained. The TTO method appeared to be reliable in a group of Tunisian RA patients, but TTO values were poorly to moderately related to measures of QOL, functional ability, and disease activity. We think that TTO and RS are not feasible for use in RA patients.