Mind · Reasoning
Fermi
Estimation via decomposition
Definition
Mechanism
Decomposed Estimation: break unknown quantity into factors you can Estimate. Multiply factors. Accept order-of-magnitude accuracy. Example: "pianos in Chicago" = population × household fraction × piano-owning fraction. Errors often cancel across factors. It invokes Decompose to break an unknown quantity into estimable sub-factors.
Invariants
- Error Cancellation: Overestimation in sub-factors tends to cancel underestimation
- Geometric Mean: Final estimate is geometric mean of bounds
Risks
Failure modes
Correlated Error Stacking
If all sub-estimates are biased in the same direction (e.g., all optimistic), the errors compound rather than cancel.
Relationships
Builds on
Nothing in this library builds on this pattern yet.
Reference
Parameters
confidence_intervalPercentage, [50%, 95%]- Target coverage of true value
decomposition_depthInteger, [2, 6]- Estimation chain length