---
slug: "Fermi"
name: "Fermi"
type: "Reasoning"
layer: "Mind"
ref: "Fermi#f206"
sema_id: "sema:Fermi#mh:SHA-256:f206e74f19af3eb55825b02c2192779a627ddff7b1c465a09d73431b863232db"
tags: ["Mind","Reasoning"]
updated: 2026-11-11
mindscape: "bootstrap"
index_url: https://mindscape.world/scapes/bootstrap.json
url: https://mindscape.world/bootstrap/Fermi/
related: ["Decompose","Estimate"]
---

# Fermi

Estimation via decomposition

Layer: Mind · Category: Reasoning

## Mechanism

Decomposed Estimation: break unknown quantity into factors you can [Estimate](https://mindscape.world/scapes/bootstrap/Estimate.md). 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](https://mindscape.world/scapes/bootstrap/Decompose.md) 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

## 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.

## Parameters

- `confidence_interval` (Percentage, [50%, 95%]): Target coverage of true value
- `decomposition_depth` (Integer, [2, 6]): Estimation chain length

## Builds on

- [Decompose](https://mindscape.world/scapes/bootstrap/Decompose.md) (Mind; Composes with)
- [Estimate](https://mindscape.world/scapes/bootstrap/Estimate.md) (Mind; Composes with)

## Used by

—

## Identity

- Sema ID: `sema:Fermi#mh:SHA-256:f206e74f19af3eb55825b02c2192779a627ddff7b1c465a09d73431b863232db`
- Ref: `Fermi#f206`
- Supersedes:
  - `sema:Fermi#mh:SHA-256:1e06d04bfff04954ad09852a7a4b1b583acc76c431dc926b4afe3cce5abfe210`
  - `sema:Fermi#mh:SHA-256:128b7131810fba03748bcc5dce657248d5547beeb23e87750cd76e6e59a80bd5`
  - `sema:Fermi#mh:SHA-256:964a2d4f8166deefb544d347da4f4c36b2c32885bb24f2f3e36cd3361638c9c2`
  - `sema:Fermi#mh:SHA-256:688559c783f162aee4fc61fd380bd30094219d76a844a6a9efce9ae1feeaf622`

## Links

- [Pattern page](https://mindscape.world/bootstrap/Fermi/)
- [View in the interactive graph](https://mindscape.world/bootstrap/#Fermi)
- [JSON](https://mindscape.world/scapes/bootstrap/Fermi.json)
- [Index of all patterns](https://mindscape.world/scapes/bootstrap.json)