Modifying the Composite Time Trade-Off Method to Improve Its Discriminatory Power

Abstract

Objectives: In cost-effectiveness analysis of health technologies, health state utilities are needed. They are often elicited with a composite time trade-off (cTTO) method, particularly for the widely used EQ-5D-5L. Unfortunately, cTTO discriminatory power is hindered by (1) respondents' nontrading (NT) of time for quality, (2) censoring of utilities at -1, and (3) poor correlation of negative utilities with state severity. We investigated whether modifying cTTO can mitigate these effects.

Methods: We interviewed online 478 students (February to April, 2021) who each valued the same 10 EQ-5D-5L health states in 1 of 3 arms. Arm A used a standard cTTO, expanded with 2 questions to explore reasons for NT and censoring. Arms B and C used a time trade-off with modified alternatives offered to overcome loss aversion, to unify the tasks for positive and negative utilities, and to enable eliciting utilities < -1.

Results: In arms B and C, we observed less NT than in A (respectively, 4% and 4% vs 10%), more strictly negative utilities (38% and 40% vs 25%), and more utilities ≤ -1 (18% and 30% vs 10%). The average utility of state 55555 dropped to -2.15 and -2.52 from -0.53. Enabling finer trades in arm A reduced NT by 70%. Arms B and C yielded an intuitive association between negative utilities and state severity. These arms were considered more difficult and resulted in more inconsistencies.

Conclusions: The discriminatory power of cTTO can be improved, but it may require increasing the difficulty of the task. The standard cTTO may overestimate the utilities, especially of severe states.

Keywords: health state utility values; lexicographic preferences; loss aversion; time trade-off; worse than dead states.