In my paper for this journal earlier this year (Abelson, 2020), I discussed how seven official guides to benefit-cost analysis (BCA) and the leading international text on BCA (Boardman et al., 2018) deal with eight contentious issues: the issue of standing, core valuation principles, the scope of CBA, changes in real values over time, the marginal excess tax burden, the social discount rate, the use of benefit-cost ratios, and the treatment of risk. I did not discuss, however, arguably the most potent cause of poor BCA studies: appraisal optimism, which is sometimes referred to less courteously as appraisal bias. Indeed, appraisal optimism receives little attention in most BCA textbooks and official guides. I will attempt here a partial rectification of these omissions.
I start with some substantial evidence for appraisal optimism in project evaluations. I then discuss the alleged two main drivers: cognitive biases and incentives in government appraisal processes. Finally, I discuss some remedies. But I am not optimistic that the virus will entirely disappear.