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Five things you should know about cost overrun


  • Flyvbjerg, Bent
  • Ansar, Atif
  • Budzier, Alexander
  • Buhl, Søren
  • Cantarelli, Chantal
  • Garbuio, Massimo
  • Glenting, Carsten
  • Holm, Mette Skamris
  • Lovallo, Dan
  • Lunn, Daniel
  • Molin, Eric
  • Rønnest, Arne
  • Stewart, Allison
  • van Wee, Bert


This paper gives an overview of good and bad practice for understanding and curbing cost overrun in large capital investment projects, with a critique of Love and Ahiaga-Dagbui (2018) as point of departure. Good practice entails: (a) Consistent definition and measurement of overrun; in contrast to mixing inconsistent baselines, price levels, etc. (b) Data collection that includes all valid and reliable data; as opposed to including idiosyncratically sampled data, data with removed outliers, non-valid data from consultancies, etc. (c) Recognition that cost overrun is systemically fat-tailed; in contrast to understanding overrun in terms of error and randomness. (d) Acknowledgment that the root cause of cost overrun is behavioral bias; in contrast to explanations in terms of scope changes, complexity, etc. (e) De-biasing cost estimates with reference class forecasting or similar methods based in behavioral science; as opposed to conventional methods of estimation, with their century-long track record of inaccuracy and systemic bias. Bad practice is characterized by violating at least one of these five points. Love and Ahiaga-Dagbui violate all five. In so doing, they produce an exceptionally useful and comprehensive catalog of the many pitfalls that exist, and must be avoided, for properly understanding and curbing cost overrun.

Suggested Citation

  • Flyvbjerg, Bent & Ansar, Atif & Budzier, Alexander & Buhl, Søren & Cantarelli, Chantal & Garbuio, Massimo & Glenting, Carsten & Holm, Mette Skamris & Lovallo, Dan & Lunn, Daniel & Molin, Eric & Rønnes, 2018. "Five things you should know about cost overrun," Transportation Research Part A: Policy and Practice, Elsevier, vol. 118(C), pages 174-190.
  • Handle: RePEc:eee:transa:v:118:y:2018:i:c:p:174-190
    DOI: 10.1016/j.tra.2018.07.013

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    References listed on IDEAS

    1. Dan Lovallo & Carmina Clarke & Colin Camerer, 2012. "Robust analogizing and the outside view: two empirical tests of case‐based decision making," Strategic Management Journal, Wiley Blackwell, vol. 33(5), pages 496-512, May.
    2. Leavitt, Dan & Ennis, Sean & McGovern, Pat, 1993. "The Cost Escalation of Rail Projects: Using Previous Experience to Re-Evaluate the CalSpeed Estimates," University of California Transportation Center, Working Papers qt2rt1w7xj, University of California Transportation Center.
    3. Daniel Kahneman & Dan Lovallo, 1993. "Timid Choices and Bold Forecasts: A Cognitive Perspective on Risk Taking," Management Science, INFORMS, vol. 39(1), pages 17-31, January.
    4. Cantarelli, C.C. & Molin, E.J.E. & van Wee, B. & Flyvbjerg, B., 2012. "Characteristics of cost overruns for Dutch transport infrastructure projects and the importance of the decision to build and project phases," Transport Policy, Elsevier, vol. 22(C), pages 49-56.
    5. Cantarelli, C.C. & Flyvbjerg, B. & Buhl, S.L., 2012. "Geographical variation in project cost performance: the Netherlands versus worldwide," Journal of Transport Geography, Elsevier, vol. 24(C), pages 324-331.
    6. Li Liu & Zigrid Napier, 2010. "The accuracy of risk-based cost estimation for water infrastructure projects: preliminary evidence from Australian projects," Construction Management and Economics, Taylor & Francis Journals, vol. 28(1), pages 89-100.
    7. Awojobi, Omotola & Jenkins, Glenn P., 2016. "Managing the cost overrun risks of hydroelectric dams: An application of reference class forecasting techniques," Renewable and Sustainable Energy Reviews, Elsevier, vol. 63(C), pages 19-32.
    8. Robert F. Bordley, 2014. "Reference Class Forecasting: Resolving Its Challenge to Statistical Modeling," The American Statistician, Taylor & Francis Journals, vol. 68(4), pages 221-229, November.
    9. Krugman, Paul, 2000. "How Complicated Does the Model Have to Be?," Oxford Review of Economic Policy, Oxford University Press, vol. 16(4), pages 33-42, Winter.
    10. Morten Welde & James Odeck, 2017. "Cost escalations in the front-end of projects – empirical evidence from Norwegian road projects," Transport Reviews, Taylor & Francis Journals, vol. 37(5), pages 612-630, September.
    11. Bent Flyvbjerg, 2009. "Survival of the unfittest: why the worst infrastructure gets built--and what we can do about it," Oxford Review of Economic Policy, Oxford University Press, vol. 25(3), pages 344-367, Autumn.
    12. Flyvbjerg, Bent, 2016. "The Fallacy of Beneficial Ignorance: A Test of Hirschman’s Hiding Hand," World Development, Elsevier, vol. 84(C), pages 176-189.
    13. Bent Flyvbjerg & Allison Stewart & Alexander Budzier, 2016. "The Oxford Olympics Study 2016: Cost and Cost Overrun at the Games," Papers 1607.04484,
    14. Bent Flyvbjerg, 2013. "Quality Control and Due Diligence in Project Management: Getting Decisions Right by Taking the Outside View," Papers 1302.2544,
    15. Love, Peter E.D. & Ahiaga-Dagbui, Dominic D., 2018. "Debunking fake news in a post-truth era: The plausible untruths of cost underestimation in transport infrastructure projects," Transportation Research Part A: Policy and Practice, Elsevier, vol. 113(C), pages 357-368.
    16. Bent Flyvbjerg & Alexander Budzier, 2018. "Report for the Edinburgh Tram Inquiry," Papers 1805.12106,
    17. Atif Ansar & Bent Flyvbjerg & Alexander Budzier & Daniel Lunn, 2016. "Does infrastructure investment lead to economic growth or economic fragility? Evidence from China," Oxford Review of Economic Policy, Oxford University Press, vol. 32(3), pages 360-390.
    18. Bent Flyvbjerg, 2014. "What You Should Know About Megaprojects, and Why: An Overview," Papers 1409.0003,
    19. Ansar, Atif & Flyvbjerg, Bent & Budzier, Alexander & Lunn, Daniel, 2014. "Should we build more large dams? The actual costs of hydropower megaproject development," Energy Policy, Elsevier, vol. 69(C), pages 43-56.
    20. Chantal C Cantarelli & Bent Flyvbjerg & Bert van Wee & Eric J E Molin, 2010. "Lock-in and its Influence on the Project Performance of Large-Scale Transportation Infrastructure Projects: Investigating the Way in Which Lock-in Can Emerge and Affect Cost Overruns," Environment and Planning B, , vol. 37(5), pages 792-807, October.
    21. Welton Chang & Eva Chen & Barbara Mellers & Philip Tetlock, 2016. "Developing expert political judgment: The impact of training and practice on judgmental accuracy in geopolitical forecasting tournaments," Judgment and Decision Making, Society for Judgment and Decision Making, vol. 11(5), pages 509-526, September.
    22. Smith, Stanley K., 1997. "Further thoughts on simplicity and complexity in population projection models," International Journal of Forecasting, Elsevier, vol. 13(4), pages 557-565, December.
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    Cited by:

    1. Flyvbjerg, Bent & Ansar, Atif & Budzier, Alexander & Buhl, Søren & Cantarelli, Chantal & Garbuio, Massimo & Glenting, Carsten & Holm, Mette Skamris & Lovallo, Dan & Molin, Eric & Rønnest, Arne & Stewa, 2019. "On de-bunking “Fake News” in the post-truth era: How to reduce statistical error in research," Transportation Research Part A: Policy and Practice, Elsevier, vol. 126(C), pages 409-411.
    2. Love, Peter E.D. & Ika, Lavagnon A. & Ahiaga-Dagbui, Dominic D., 2019. "On de-bunking ‘fake news’ in a post truth era: Why does the Planning Fallacy explanation for cost overruns fall short?," Transportation Research Part A: Policy and Practice, Elsevier, vol. 126(C), pages 397-408.
    3. Giuliano Marella & Valentina Antoniucci, 2019. "Time Overrun in Public Works—Evidence from North-East Italy," Sustainability, MDPI, Open Access Journal, vol. 11(24), pages 1-1, December.
    4. Penyalver, Domingo & Turró, Mateu & Williamson, John B., 2019. "Measuring the value for money of transport infrastructure procurement; an intergenerational approach," Transportation Research Part A: Policy and Practice, Elsevier, vol. 119(C), pages 238-254.
    5. Lozano, Jorge-Mario & Zuluaga, Santiago & Sánchez-Silva, Mauricio, 2020. "Developing flexible management strategies in infrastructure: The sequential expansion problem for infrastructure analysis (SEPIA)," Reliability Engineering and System Safety, Elsevier, vol. 200(C).
    6. Ginés de Rus & Javier Campos & Daniel Graham & M. Pilar Socorro & Jorge Valido, 2020. "Evaluación Económica de Proyectos y Políticas de Transporte: Metodología y Aplicaciones. Parte 1: Metodología para el análisis coste-beneficio de proyectos y políticas de transporte," Working Papers 2020-11, FEDEA.


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