Optimism Bias in Multilateral Development Banks’ Infrastructure Appraisals

Parra López, Carlos (2026): Optimism Bias in Multilateral Development Banks’ Infrastructure Appraisals.

Abstract

The appropriateness of using Cost-Benefit Analysis as a decision-making criterion in transport infrastructure planning has been widely questioned due to systematic deviations from appraisal estimates—primarily in investment costs, delivery times, and demand forecasts—and a persistent optimism bias among evaluators that leads to projects with negative social returns, commonly referred to as white elephants. However, there remains relatively little empirical evidence on the extent to which social profitability is affected by these deviations, largely because ex-post evaluations are seldom conducted. In this study, we construct a dataset of infrastructure projects evaluated and financed by Multilateral Development Banks (MDBs) and find that deviations remain modest relative to other studies and evaluators. Most indicators suggest that project profitability is unbiased and that only a relatively small proportion of projects yield negative social returns. We argue that this outcome may be attributed to the MDBs’ internal appraisal policies, particularly regarding project governance (with the banks acting as both evaluators and financiers, and applicant countries serving as project sponsors and executioners) and the mandatory implementation of ex-post evaluations, suggesting that the optimism bias phenomenon is more related to strategic misrepresentation than to a cognitive bias.

• Item Type: MPRA Paper
• Language: English
• Keywords: Optimism bias, strategic misrepresentation, Cost-Benefit Analysis, project appraisal, ex-post revisions.
• Subjects: R - Urban, Rural, Regional, Real Estate, and Transportation Economics > R4 - Transportation Economics > R42 - Government and Private Investment Analysis ; Road Maintenance ; Transportation Planning

References

Asplund, D., & Eliasson, J. (2016). Does uncertainty make cost-benefit analyses pointless? Transportation Research Part A: Policy and Practice, 92, 195–205. https://doi.org/10.1016/j.tra.2016.08.002 Autoridad Independiente de Responsabilidad Fiscal (AIReF). (2020). Spending Review Infraestructuras de transporte. Benitez, D., Estache, A., & Søreide, T. (2010). Dealing with Politics for Money and Power in Infrastructure (Working Paper 5455; Policy Research). http://econ.worldbank.org. Boardman, A., L. Mallery, W., & Vinin, A. (1994). Learning from ex ante/ex post Cost-Benefit Comparisons: the Coquihalla Highway Example. Socio-Economic Planning Sciences, 28(2), 69–84. Bos, E., & de Swart, L. (2024). Towards a better comparison of ex-post and ex-ante BCA’s by decomposing potential causes of difference. Transport Policy, 151, 36–45. Cantarelli, C. C., Flyvbjerg, B., Molin, E. J. E., & Van Wee, B. (2010). Cost overruns in Large-Scale Transportation Infrastructure Projects: Explanations and Their Theoretical Embeddedness. European Journal of Transport and Infrastructure Research, 10(1), 5–18. http://www.ejtir.tbm.tudelft.nl/issues/2010_01 Changali, S., Mohammad, A., & Van Nieuwland, M. (2015). The construction productivity imperative. de Jong, G., Vignetti, S., & Pancotti, C. (2020). Ex-post evaluation of major infrastructure projects. Transportation Research Procedia, 42, 75–84. https://doi.org/10.1016/j.trpro.2019.12.008 de Rus, G., & Socorro, M. P. (2010). Infrastructure investment and incentives with supranational funding. Transition Studies Review, 17(3), 551–567. https://doi.org/10.1007/s11300-010-0163-1 de Rus, G., & Socorro, M. P. (2017). Planning, evaluation and financing of transport infrastructures: Rethinking the basics. Review of Network Economics, 16(2), 143–160. Del Bo, C., & Florio, M. (2010). Cost-Benefit Analysis and the Rates of Return of Infrastructure Projects: Evidence from International Organizations. Transition Studies Review, 17(3), 587–610. https://doi.org/10.1007/s11300-010-0162-2 Dellarocas, C., Dini, F., & Spagnolo, G. (2006). Designing reputation mechanisms. In Handbook of Procurement (pp. 446–482). Cambridge University Press. https://doi.org/10.1017/cbo9780511492556.019 Department for Transport (DfT). (2021). Updating the Evidence Behind the Optimism Bias Uplifts for Transport Appraisals. Driscoll, P. A., & Nicolaisen, M. S. (2014). Ex-Post Evaluations of Demand Forecast Accuracy: A Literature Review. Transport Reviews, 34(4), 540–557. https://doi.org/10.1080/01441647.2014.926428 Engel, E., Fischer, R. D., & Galetovic, A. (2014). The Economics of Public-Private Partnerships: A Basic Guide. Cambridge University Press. European Commission, D.-G. for R. and U. policy (DG R. (2023). Handbook on selection of operations: Towards simplification - Analysis of selection of operations. Taking stock of practices in the EU Member States. European Commission, D.-G. for R. and U. policy (DG R. (2025). Ex post evaluation of the European Regional Development Fund (ERDF) and the Cohesion Fund for the programming period 2014-2020. Flyvbjerg, B. (2008). Curbing optimism bias and strategic misrepresentation in planning: Reference class forecasting in practice. European Planning Studies, 16(1), 3–21. https://doi.org/10.1080/09654310701747936 Flyvbjerg, B., & Bester, D. W. (2021). The Cost-Benefit Fallacy: Why Cost-Benefit Analysis Is Broken and How to Fix It. Journal of Benefit-Cost Analysis, 12(3), 395–419. https://doi.org/10.1017/bca.2021.9 Flyvbjerg, B., Holm, M. S., & Buhl, S. (2002). Underestimating costs in public works projects: Error or lie? Journal of the American Planning Association, 68(3), 279–295. https://doi.org/10.1080/01944360208976273 Gómez-Lobo, A. (2012). Institutional Safeguards for Cost Benefit Analysis: Lessons from the Chilean National Investment System. Journal of Benefit-Cost Analysis, 3(1), 1–30. https://doi.org/10.1515/2152-2812.1102 Highways England. (2015). Post Opening Project Evaluation (POPE) of Major Schemes. Main Report Meta-analysis 2015. Independent Evaluation Group (IEG), W. B. G. (2010). Cost-Benefit Analysis in World Bank Projects. Independent Evaluation Group (IEG), W. B. G. (2024). Guidance Manual for Independent Evaluation Group Validators Implementation Completion and Results Report Reviews for Investment Project Financing. International Transport Forum (ITF), O. for E. C. and D. (OECD). (2017). Ex-Post Assessment of Transport Investments and Policy Interventions (ITF Roundtable Reports). OECD. https://doi.org/10.1787/9789282108154-en International Transport Forum (ITF), O. for E. C. and D. (OECD). (2021). Developing Strategic Approaches to Infrastructure Planning. www.itf-oecd.org Levinson, D., & Wang, Y. (2023). The accuracy of benefit-cost analysis for transport projects supported by the Asian Development Bank. Asian Transport Studies, 9. https://doi.org/10.1016/j.eastsj.2023.100104 Limodio, N. (2011). The Success of Infrastructure Projects in Low-Income Countries and the Role of Selectivity (5694; Policy Research Working Paper). http://econ.worldbank.org. Mackie, P., & Preston, J. (1998). Twenty-one sources of error and bias in transport project appraisal. Transport Policy, 5, 1–7. Ministère de l’Écologie, du D. D. et de l’Énergie (MEDDE). (2021). Bilan des bilans LOTI. Rapport no 012979-01. Odeck, J., & Kjerkreit, A. (2019). The accuracy of benefit-cost analyses (BCAs) in transportation: An ex-post evaluation of road projects. Transportation Research Part A: Policy and Practice, 120, 277–294. https://doi.org/10.1016/j.tra.2018.12.023 Parra, C. (2025). Shortfalls in profitability: Internal Rate of Return re-estimation based on ex-ante indicators and ex-post deviations (126981; MPRA Paper). Pohl, G., & Mihaljek, D. (1992). Project Evaluation and Uncertainty in Practice: A Statistical Analysis of Rate-of-Return Divergences of 1,015 World Bank Projects. World Bank Economin Review, 6(2), 255–277. World Bank. (2005). Transport Note No. TRN-6 Notes on the Economic Evaluation of Transport Projects When and How to Use NPV, IRR and Modified IRR. World Bank. (2023). Bank Directive Investment Project Financing (OPS5.03-DIR.117). World Bank. (2025). The Worldwide Governance Indicators: Revised Methodology for Measuring Governance Using Perception Data Acknowledgement. Worsley, T. (2015). Ex-post Assessment of Transport Investments and Policy Interventions (2014–19; International Transport Forum Discussion Paper). www.internationaltransportforum.org/jtrc/DiscussionPapers/jtrcpapers.html