How Big Things Get Done: The Surprising Factors Behind Every Successful Project, from Home Renovations to Space Exploration

by Professor Bent Flyvbjerg

I came to call this process “reference-class forecasting” (RCF).11 After I developed it for Gordon Brown, the British government used it to forecast the time and cost of major projects and was so satisfied with the results that it made the process mandatory.12 Denmark did the same.13 RCF has also been used in the public and private sectors in the United States, China, Australia, South Africa, Ireland, Switzerland, and the Netherlands.14 All that experience has enabled rigorous testing, and a slew of independent studies has confirmed that “RCF indeed performs the best,” in the words of one.15 It performs the best by a large margin. The gap between a conventional forecast and one that uses RCF varies by project type, but for over half the projects for which we have data, RCF is better by 30 percentage points or more. That’s on average. A 50 percent increase in accuracy is common. Improvements of more than 100 percent are not uncommon.