The value of correcting values: influence and importance of correcting TTO scores for time preference

Quality-adjusted life year (QALY) values measured by means of the time tradeoff (TTO) method are often used in economic evaluations. However, these values are mostly not corrected for time preference, i.e., a lower valuation being attached to later life years than to earlier life years, and therefore may underestimate the true QALY weights. Moreover, the magnitude of the underestimation depends on the severity of the health state and the horizon chosen in the TTO method. Hence, we cannot just add a constant component to all existing QALY tariffs. In this study, we estimated the value of correcting TTO scores. We showed the possible consequences for health policymaking when we correct TTO scores for time preference, thereby taking into account severity and horizon.

We employed the results obtained using a nonparametric time preference elicitation method. We made use of experimental time preference data, in order to better represent individuals' time preferences.

Our results demonstrate that correcting for time preference does not result in one clear influence on the QALY gains from health changes. When considering these changes in the context of cost-utility ratios, the proportional change in the QALY gain is crucial.

Correcting TTO scores has a moderate, yet nonnegligible influence on outcomes. We conclude that correcting TTO scores for time preference is feasible and influential, so that there can be a substantial value of correcting values for time preference.