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Rare Disasters, Tail-Hedged Investments, and Risk-Adjusted Discount Rates

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  • Martin L. Weitzman

Abstract

What is the best way to incorporate a risk premium into the discount rate schedule for a real investment project with uncertain payoffs? The standard CAPM formula suggests a beta-weighted average of the return on a safe investment and the mean return on an economy-wide representative risky investment. Suppose, though, that the project constitutes a tail-hedged investment, meaning that it is expected to yield positive payoffs in catastrophic states of nature. Then the model of this paper suggests that what should be combined in a weighted average are not the two discount rates, but rather the corresponding two discount factors. This implies an effective discount rate schedule that declines over time from the standard CAPM formula down to the riskfree rate alone. Some simple numerical examples are given. Implications are noted for discounting long-term public investments and calculating the social cost of carbon in climate change.

Suggested Citation

  • Martin L. Weitzman, 2012. "Rare Disasters, Tail-Hedged Investments, and Risk-Adjusted Discount Rates," NBER Working Papers 18496, National Bureau of Economic Research, Inc.
  • Handle: RePEc:nbr:nberwo:18496
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    Cited by:

    1. Lars Hultkrantz, 2021. "Discounting in economic evaluation of healthcare interventions: what about the risk term?," The European Journal of Health Economics, Springer;Deutsche Gesellschaft für Gesundheitsökonomie (DGGÖ), vol. 22(3), pages 357-363, April.
    2. Gollier, Christian, 2012. "A theory of rational short-termism with uncertain betas," LERNA Working Papers 12.14.371, LERNA, University of Toulouse.
    3. Hultkrantz, Lars & A. Krüger, Niclas & Mantalos, Panagiotis, 2014. "Risk-adjusted long-term social rates of discount for transportation infrastructure investment," Research in Transportation Economics, Elsevier, vol. 47(C), pages 70-81.
    4. Stefano Giglio & Matteo Maggiori & Johannes Stroebel, 2016. "No‐Bubble Condition: Model‐Free Tests in Housing Markets," Econometrica, Econometric Society, vol. 84, pages 1047-1091, May.
    5. Christian Gollier, 2012. "Evaluation of Long-Dated Investments under Uncertain Growth Trend, Volatility and Catastrophes," CESifo Working Paper Series 4052, CESifo.
    6. Isoré, Marlène & Szczerbowicz, Urszula, 2017. "Disaster risk and preference shifts in a New Keynesian model," Journal of Economic Dynamics and Control, Elsevier, vol. 79(C), pages 97-125.
    7. Stefano Giglio & Matteo Maggiori & Johannes Stroebel, 2014. "Very long-run discount rates," Globalization Institute Working Papers 182, Federal Reserve Bank of Dallas.
    8. Panagiotis Mantalos & Lars Hultkrantz, 2018. "Estimating ‘gamma’ for tail-hedge discount rates when project returns are cointegrated with GDP," Applied Economics, Taylor & Francis Journals, vol. 50(37), pages 4074-4085, August.
    9. Gollier, Christian, 2016. "Evaluation of long-dated assets: The role of parameter uncertainty," Journal of Monetary Economics, Elsevier, vol. 84(C), pages 66-83.
    10. Stefano Giglio & Bryan Kelly & Johannes Stroebel, 2021. "Climate Finance," Annual Review of Financial Economics, Annual Reviews, vol. 13(1), pages 15-36, November.
    11. Hultkrantz, Lars & Mantalos, Panagiotis, 2018. "Hedging with trees: Tail-hedge discounting of long-term forestry returns," Journal of Forest Economics, Elsevier, vol. 30(C), pages 52-57.
    12. Gollier, Christian, 2012. "Asset pricing with uncertain betas: A long-term perspective," TSE Working Papers 12-354, Toulouse School of Economics (TSE).
    13. Serban Raicu & Mihaela Popa & Dorinela Costescu, 2022. "Uncertainties Influencing Transportation System Performances," Sustainability, MDPI, vol. 14(13), pages 1-15, June.
    14. Bernard Lapeyre & Emile Quinet, 2017. "A Simple GDP-based Model for Public Investments at Risk," Post-Print hal-01666574, HAL.
    15. Johannes Stroebel & Jeffrey Wurgler, 2021. "What Do You Think about Climate Finance?," CESifo Working Paper Series 9350, CESifo.
    16. Kathrin Goldmann, 2019. "Time-declining risk-adjusted social discount rates for transport infrastructure planning," Transportation, Springer, vol. 46(1), pages 17-34, February.
    17. Andersson, Henrik & Hultkrantz, Lars & Lindberg, Gunnar & Nilsson, Jan-Eric, 2017. "The role of economic analysis for investment priorities in Sweden’s transport sector," Working papers in Transport Economics 2017:12, CTS - Centre for Transport Studies Stockholm (KTH and VTI), revised 23 May 2018.
    18. Giglio, Stefano & Maggiori, Matteo & Stroebel, Johannes & Tan, Zhenhao & Utkus, Stephen & Xu, Xiao, 2023. "Four Facts About Esg Beliefs And Investor Portfolios," SocArXiv dcb93, Center for Open Science.
    19. Rob Aalbers, 2013. "Optimal Discount Rates for Investments in Mitigation and Adaptation," CPB Discussion Paper 257.rdf, CPB Netherlands Bureau for Economic Policy Analysis.
    20. Corneo, Giacomo, 2015. "Volkswirtschaftliche Bewertung öffentlicher Investitionen," Discussion Papers 2015/12, Free University Berlin, School of Business & Economics.
    21. Bernard Lapeyre & Emile Quinet, 2017. "A Simple GDP-based Model for Public Investments at Risk," PSE-Ecole d'économie de Paris (Postprint) hal-01666574, HAL.
    22. Rob Aalbers, 2013. "Optimal Discount Rates for Investments in Mitigation and Adaptation," CPB Discussion Paper 257, CPB Netherlands Bureau for Economic Policy Analysis.

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    More about this item

    JEL classification:

    • E43 - Macroeconomics and Monetary Economics - - Money and Interest Rates - - - Interest Rates: Determination, Term Structure, and Effects
    • G11 - Financial Economics - - General Financial Markets - - - Portfolio Choice; Investment Decisions
    • G12 - Financial Economics - - General Financial Markets - - - Asset Pricing; Trading Volume; Bond Interest Rates
    • Q54 - Agricultural and Natural Resource Economics; Environmental and Ecological Economics - - Environmental Economics - - - Climate; Natural Disasters and their Management; Global Warming

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