Using the Choice Sequence in Time Trade-Off as Discrete Choices: Do the Two Stories Match?

The EQ-5D-5L valuation protocol recommends combining time trade-off (TTO) and discrete choice experiments (DCEs). DCEs that include a duration attribute (DCE_TTO) allow modeling on the quality-adjusted life-year scale. Because the choice sequence in a TTO can be construed as a series of DCE_TTO, we used data from a single TTO study to investigate the extent to which DCE values match TTO values when based on identical preferences.

In a TTO design in which a fixed set of choices were administered without termination at preference indifference, 202 individuals each valued 10 EQ-5D health states. From identified indifference points, we estimated three sets of TTO values: (i) plotting means and (ii) applying censored regressions at -1 and 1. Using all strict preferences, we (iii) estimated DCE_TTO values with a logit model and a bootstrap procedure.

Estimated DCE_TTO and TTO values agreed well at the severe end of the quality-adjusted life-year scale, but with decreasing severity, DCE_TTO values were higher than TTO-values, with the difference peaking at 0.37 for the mildest health state. Left-censoring TTO values at -1 worsen the agreement for the worst health states and did not affect health states. Right censoring at 1 improved the agreement for mild states.

TTO and the DCE_TTO values estimated from the same preference data diverged, with increasing difference for milder health states. Although the values converged when applying censored regression at +1, we question the validity of this adjustment.