Does the Planning Fallacy Prevail in Social Infrastructure Projects? Empirical Evidence and Competing Explanations

The planning fallacy is at play in projects when optimism bias and/or strategic misrepresentation are present. We examine the cost performance of approximately US$ 6.5 billion worth of social infrastructure projects that were procured in Hong Kong and specifically the differences between their final accounts and the various types of estimates that were prepared prior to construction. We focus on the (honest) planning fallacy and hence aim to determine whether estimates are more optimistic than actual costs. Our data shows that 43% of projects incurred a cost underrun from their contract award. We therefore infer that at best 57% of projects may be explained by the presence of the planning fallacy. Based on our findings, we argue that optimism and pessimism bias coexist. Likewise, the planning fallacy and competing explanations can simultaneously account for cost deviations in social infrastructure projects. We submit that the prevalence of the planning fallacy has been exaggerated and hence provide an explanation as to why this has occurred. We finally suggest there is a need for additional empirical work to test the claim that the planning fallacy is the underlying cause of cost overruns and thus the best “theory” to explain “how projects work.”