Assumptions and method
The familiar 80/20 ratio is not a law. Frequency alone can conceal rare, severe failures.
Test a scenario
Use the result in a decision
Agree acceptance criteria and distinguish variation from a meaningful signal.
The familiar 80/20 ratio is not a law. Frequency alone can conceal rare, severe failures.
Set a baseline and change one assumption to compare outcomes.
A worked example
Follow the fixed teaching example
- Counts sum to 18 + 11 + 7 + 4 = 40.
- The first category contributes 18/40 = 45%; the first two contribute 29/40 = 72.5%.
These illustrative inputs describe a project scenario, not a published benchmark. All monetary inputs use the same currency and price basis.
- One row: category, count
- Rework, 18 Missing input, 11 Approval delay, 7 Other, 4
- Total
- 40
| Category | Count | Cumulative % |
|---|---|---|
| Rework | 18 | 45 |
| Missing input | 11 | 72.5 |
| Approval delay | 7 | 90 |
| Other | 4 | 100 |
Interpret the output only within the assumptions above. Changing the inputs changes the result; it does not validate the inputs.
Source & credit
Standard mathematical statistics; the handbook is an authoritative technical reference, not a claim of sole origin.
NIST/SEMATECH: statistical methods
This is independently written code and explanation of the underlying method. The linked publication, its diagrams and its trademarks remain its owner’s material; no permission to reuse them is implied.