The Time Trade-Off (TTO) is an instrument used for valuing health-related quality of life. This study evaluated the test-retest reliability of a computer TTO in rheumatoid arthritis (RA), and compared the computer with the interview TTO regarding feasibility and agreement.
In study 1 using a cross-over design, thirty patients completed both TTOs. In study 2, twenty-nine other patients completed the computer TTO twice to examine test-retest reliability. Feasibility was measured by assessing actual and perceived time duration and general experience of the patient. Agreement between utility scores of both TTOs was measured by Bland-Altman analysis.
Both TTOs were feasible. The computer TTO showed high test-retest reliability (ICC = 0.88). Bland-Altman analysis showed a small mean difference (0.06, SD = 0.14, effect size=0.30) between both TTOs. Limits of agreement were wide (-0.22 to 0.34). Differences between interview and computer TTO utilities did not vary over the range of scores.
The computer TTO was feasible and reliable, but did not provide similar results as the interview TTO. However, no systematic biases in the differences were found over the range of scores.