Elsevier

Value in Health

Volume 26, Issue 2, February 2023, Pages 280-291
Value in Health

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

https://doi.org/10.1016/j.jval.2022.08.011Get rights and content
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Highlights

  • Composite time trade-off (cTTO) method used to elicit utility values for health states has limited discriminatory power due to some respondents not trading time for quality for mild states, multiple observations being censored at −1 for severe states, and counterintuitive lack of association between the negative part of utility and state severity.

  • We show how changing cTTO can help to overcome all the above 3 phenomena. Offering smaller trades or changing the framing to avoid loss aversion induces trading. Making a task more consistent across better than dead and worse than dead parts restores the association between the negative utility and state severity. The changes result in much lower utility values.

  • The values elicited with cTTO may overestimate the utility. In consequence, the value of health-related quality of life improvements from severe states may be underestimated, and the value of life prolonging treatments in impaired health may be overestimated, whereas the health interventions offering small health-related quality of life gains for small incremental costs may be artificially disadvantaged.

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

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