Employing Episodic Future Thinking to Reduce the Distortion of Time Preference in Time Trade-Off Valuation

OBJECTIVES: Previous research has found that the composite time trade-off (cTTO) method is influenced by time preferences. More specifically, cTTO results are typically biased downward if not adjusted for discounting of future life years. Most previous research that did correct for this distortion, only did so after the task is completed. Employing such a correction may increase noise in TTO results or, if the same amount of discounting is assumed for all respondents, neglecting individual heterogeneity in time preference. This study, therefore, aims to explore the possibility of reducing distortion ex ante hby applying Episodic Future Thinking (EFT) before the cTTO tasks commence.

METHODS: EFT is a validated protocol in psychology that facilitates detailed stimulation of potential future events in order to help reduce discounting. In this study, respondents in the EFT groups were asked to imagine life in the next 10 to 20 years, aiming to improve their ability to value future health states with more future-related emotions. For a better comparison, we utilized Episodic Recent thinking (ERT) with filler tasks in a control group, where respondents were asked to recall recent memories. 150 participants from the UK general public were recruited for personal online interviews, who were randomly and evenly assigned to the control (ERT) and treatment (EFT) group. cTTO utilities of seven EQ-5D health states were estimated by the cTTO method and time preference was measured separately by means of a nonparametric method.

RESULTS: There is no significant difference in TTO utilities and discounting between the EFT and ERT treatments. We also found no evidence in favor of EFT affecting discounting in EQ-5D-5L valuation. Correcting for discounting resulted in lower TTO utilities in the ERT group, compared to implementing the EFT task.

CONCLUSIONS: Overall, it is concluded that EFT does not affect the elicitation in EQ-5D-5L valuation.