The role of discounting type in economic modelling

This paper reviews important approaches to discounting in economic modelling. It summarizes historical approaches and discusses why exponential discounting has been adopted as a widely accepted benchmark. The article then presents hyperbolic discounting as an alternative, while stresses different interpretation of discounting in positive and normative economics. In positive economics, the paper uses recent evidence to show that some observed regularities implied by exponential discounting are counterfactual and we illustrate different implications of the two approaches to discounting using numerical simulations of a stylized model of investment-consump- tion behaviour. It also concerns with applications of discounting in normative models of environmental economics. Many authors claim that exponential discounting, when used for long-term project evaluation, leads to an unfair treatment with generations living in a far future. We construct a model of optimal non-renewable resource exploitation to illustrate different normative implications of exponential and hyperbolic discounting.