Forecast a project by the distribution of outcomes for similar past projects rather than by reasoning about this one.
Flyvbjerg's method, adopted by the UK Treasury Green Book. It works because it bypasses the inside view entirely: the question becomes what happened to projects like this, not what will happen to ours.
In practice
- A couple budgeting a wedding from what other people's weddings cost lands closer than one pricing every item themselves.
- A team that asks how long similar migrations took at other firms gets a better estimate than one that reasons carefully about its own.
- Further reading
- Wikipedia
- Subject
- Decision-making & Reasoning
- Essay
- Razors, rules and the tools of careful thought