EXPRESS: A meta-analysis of the effects of episodic future thinking on delay discounting.

Delay discounting (DD) refers to the phenomenon in which the subjective value of future rewards is reduced over time. There are individual differences in the DD rate, and increased discounting has been observed in those with various psychiatric disorders. Episodic future thinking (EFT) is the act of vividly imagining events that may happen in the future. Studies have shown that EFT could reduce DD, although inconsistent results have been reported. The aim of this meta-analysis was to clarify the efficacy with which EFT reduces DD and to identify potential moderators. Forty-seven studies (including 63 contrasts) were included in the final analysis. EFT was found to significantly reduce DD (Hedges' g =0.52). Moderator analysis showed that positive EFT (g=0.64) was more effective in reducing DD than EFT with the valence not specifically mentioned (g=0.28), and EFT with neutral or negative valence (g=-0.03). In addition, several factors related to the control task and DD task were related to the efficacy of EFT to reduce DD. These findings have implications for using EFT to reduce DD in the future.