Make a forecast that can later be checked, updated and learned from.
Open situation →Reasoning Practice · Intermediate
The risks do not add up
A team estimates a 25% chance that the project will be late. When asked separately, it gives 20% to supplier delay, 20% to testing delay and 15% to staffing delay, with overlap left undefined.
Your decision
What should the team do next?
Show the best first move
B. Define overlap and reconcile the component risks with the total probability using comparable project data.
Why this move helps
Decomposed risks can receive more probability than the undivided event. Reconciliation and a reference distribution make the forecast internally checkable.
Evidence still missing
- How risk categories overlap.
- The frequency of each cause in comparable projects.
- A rule for combining component estimates.
Evidence note
Subadditivity is a useful lens for inconsistent whole-versus-part estimates. The numbers may also reflect unclear definitions rather than a stable cognitive effect.
Next action
Create mutually clear risk definitions and reconcile the total before publishing the forecast.
Best first lens
Subadditivity Effect
Use the lens to ask a better question. It does not prove that a person or team has a cognitive bias.
Other defensible lenses
The situation may have more than one explanation.
Continue the path
Situation → skill → technique → action.
You can produce forecasts that are easier to challenge, compare and learn from later.
Build this skill →Compare a vivid case with the broader frequency or distribution that should inform the judgment.
Run the technique →