Purpose: The time trade-off (TTO) method is frequently used to elicit health state values in national valuation studies for the EQ-5D. TTO is used to identify the point of preferential equilibrium between a fixed number of years in an impaired EQ-5D health state and a shorter life in perfect health. Values are anchored at perfect health (1) and death (0). To allow health states considered worse than death (<0), the initial TTO question asks whether the target health state is better, worse, or equal to death. It is conceivable that respondents who are opposed to euthanasia display an aversion to describing health states as worse than death, resulting in elevated TTO scores. The aim of this study was to investigate whether respondent attitudes towards euthanasia affect health state values elicited using the regular TTO method, and the Lead-Time TTO (LT-TTO), where comparison to death is less direct.
Method: Each of 811 members of a survey panel representative of the Norwegian general population valued eight EQ-5D health states on a visual-analogue scale (VAS) and with the TTO method (n=328) or with the alternative LT-TTO (n=483). We assessed attitudes towards euthanasia (ATE) using three items (passive euthanasia, active euthanasia, and assisted suicide), resulting in values ranging from -2 (strongly against euthanasia) to 2 (strongly in favour). After exclusions due to inconsistencies and incomplete responses, 400 LT-TTO and 213 regular TTO respondents were included in analyses. We used multiple linear regressions to predict VAS, TTO and LT-TTO values by ATE, sex, age and education.
Results: For VAS values, the only statistically significant predictor was sex. For regular and Lead-Time TTO, the only significant predictor was ATE; a one point increase on the ATE scale was associated with a mean TTO value of -.109 (p<.001) and .075 (p<.001) for regular and LT-TTO, respectively.
Conclusions: In this study TTO values were associated with attitudes towards euthanasia, while VAS values were not. The effect was greater for regular TTO than LT-TTO, possibly because death is less salient in the LT-TTO than the regular method. The findings indicate that the TTO method measures attitude towards death rather than, or in addition to, preferences for the health states in question.
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