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This paper sets out the alternative approaches to the public sector discount rate and explains the assumptions involved. There are two main ways of thinking about the discount rate. First, the social opportunity cost of capital approach (SOC) defines the discount rate as the rate of return that a decision-maker could earn on a hypothetical 'next best alternative' to a public investment. Second, the social rate of time preference approach (SRTP) defines the discount rate as the rate of return that a decision-maker requires in order to divert resources from use in the present, to a public investment. In an 'ideal' market, these two rates are brought into alignment in equilibrium. However, as there are no markets for public investments, there are no market signals to equate preferences for investing in such projects with rates of return. There is no completely objective way of determining public sector discount rates. Essentially the discount rate reflects how the government values the future when making decisions on behalf of society: value judgements and assumptions are necessary. The paper aims to clarify these judgements. Elements of both approaches may be relevant to many policy and operational decisions that require discounting, in which case different approaches may be relevant for different contexts. The paper also briefly considers the use of hyperbolic discounting.
We should like to thank Girol Karacaoglu for supporting this work. We also benefited from helpful discussions with many colleagues in the New Zealand Treasury and a number of other government departments. In particular we should like to thank Kirsten Jensen, Dieter Katz, Joanne Leung, Chris Parker and John Yeabsley for their helpful comments on an earlier draft of this paper.
The views, opinions, findings, and conclusions or recommendations expressed in this Working Paper are strictly those of the author(s). They do not necessarily reflect the views of the New Zealand Treasury or the New Zealand Government. The New Zealand Treasury and the New Zealand Government take no responsibility for any errors or omissions in, or for the correctness of, the information contained in these working papers. The paper is presented not as policy, but with a view to inform and stimulate wider debate.