Censoring in the time trade-off valuation of worse-than-dead EQ-5D-5L health states: can a time-based willingness-to-accept question be the solution?

Abstract

The left censoring of values at -1 by 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 a time-based willingness-to-accept (tWTA) question can be used to elicit values lower than -1 and improve the estimation of EQ-5D-5L values. 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 lower than -1, a tWTA question eliciting the indifference point between a hypothetical life (i.e. x number of years in full health followed by 10years in the health state) and immediate death was used to estimate its uncensored value. We compared the statistical characteristics of the censored and uncensored data. Four hundred and twenty-nine of 1,000 respondents were offered the tWTA question in a total of 1,071 cTTO tasks. In 79.55% of those tasks, indifference was not reached. Spearman's correlation with level summary score was -0.41 and -0.40 for negative uncensored and censored data, respectively. The logical inconsistency rates of the uncensored and censored data were 0.88% vs. 0.29%, respectively. Modelling of the uncensored data resulted in coefficients with greater uncertainty and much lower predictions. The elicitation of values lower than -1 using a tWTA question that grants more time for trading 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.