OBJECTIVES: The left censoring design of the composite time trade-off (cTTO) tasks leads to excessive amount of -1 values in some EQ-5D-5L valuation studies. This study aimed to investigate whether the elicitation of values less than -1 can solve this issue and improve the estimation of EQ-5D-5L values.

METHODS: At the end of each cTTO task in the Taiwanese EQ-5D-5L valuation study, if the value of the health state was indicated to be less than -1, a willingness-to-accept question eliciting the indifference point between a hypothetical life (i.e. x number of years in full health followed by 10 years in the health state) and immediate death was used to estimate its uncensored value. We compared the statistical characteristics of the censored and uncensored values.

RESULTS: Four hundred and twenty-nine of 1,000 respondents were offered the willingness-to-accept question in a total of 1,071 cTTO tasks. In 79.55% of those tasks, indifference was not reached. Spearman’s correlation with misery index was -0.41 and -0.40 for negative uncensored and censored values, respectively. The logical inconsistency rates of the uncensored and censored values were 0.88% vs. 0.29%, respectively. Modelling of the uncensored values resulted in coefficients with greater uncertainty and much lower predictions.

CONCLUSIONS: The elicitation of values less than -1 by granting more time to trade seems not a promising solution to the value censoring of the cTTO tasks. Other strategies for valuation of very poor health states should be explored.