This kind of bias correction is sometimes undertaken more systematically. In the United Kingdom, HM Treasury has published The Green Book, a guide on how to evaluate programs and projects. The book urges planners to address optimistic biases by applying percentage adjustments to estimates of the cost and duration of a project. These adjustments should ideally be based on an organization’s historic levels of optimism bias. If no such historical data is available, The Green Book recommends applying generic adjustment percentages for each type of project.
