Abstract
OBJECTIVES: The composite time trade-off (cTTO) method has been found to be influenced by time preferences for future life years, which typically results in a downward bias on cTTO utilities without adjustment. Contrary to prior research that adjusted for this distortion ex-post, this study takes an ex-ante approach, using Episodic Future Thinking (EFT), to potentially prevent time preference distortion. We aim to investigate the effect of EFT on time preference and cTTO utilities compared to using alternative methods. METHODS: A total of 150 participants from the UK general public were recruited for interviewer-led online interviews and randomly assigned to either the control or treatment group. In the control group, they were asked to recall recent memories using the Episodic Recent Thinking (ERT) protocol, serving as filler tasks; in the treatment group, they were asked to imagine life in the next 10 to 20 years, i.e. using an EFT protocol. Afterwards, respondents were asked to value seven EQ-5D-5L health states with cTTO tasks, followed by a nonparametric method to measure time preference. RESULTS: We observed a similar pattern of time preference across the two groups, with the majority discounting positively. EFT did not significantly affect time preference. In addition, the difference between cTTO utilities mitigated by EFT and those adjusted using the ex-post approach for time preference is minimal. CONCLUSIONS: In conclusion, EFT does not seem to mitigate time preference for life years and has negligible effect on cTTO utilities, necessitating alternative strategies for reducing bias in health utilities.