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

OBJECTIVES

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

METHODS

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 values with a logit model and a bootstrap procedure.

RESULTS

Estimated DCE and TTO values agreed well at the severe end of the quality-adjusted life-year scale, but with decreasing severity, DCE 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.

CONCLUSIONS

TTO and the DCE 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.