The Pareto principle is the observation that a relatively small number of causes often account for a large share of an outcome. The familiar “80/20 rule” is a useful shorthand, but the split does not have to be exactly 80/20. The practical purpose is prioritization: identify the few categories creating most of the cost, delay, defects or risk.
How Pareto Analysis Works
- Define the problem and measurement period.
- Group events into meaningful categories.
- Measure frequency, cost, delay or another impact measure.
- Sort categories from highest to lowest impact.
- Calculate cumulative percentage.
- Focus root-cause work on the categories contributing most.
Supply-Chain Example
| Delivery-failure cause | Cases | Cumulative share |
|---|---|---|
| Supplier late dispatch | 42 | 42% |
| Transport capacity | 28 | 70% |
| Documentation error | 15 | 85% |
| Warehouse delay | 10 | 95% |
| Other | 5 | 100% |
The first two causes account for 70% of the failures. That does not prove their root causes, but it tells the team where investigation is likely to produce the greatest initial benefit.
Where Pareto Analysis Is Useful
- Supplier defects or late deliveries
- Warehouse picking errors
- Customer complaints
- Freight-cost drivers
- Inventory value concentration
- Purchase-price variance
- Root-cause categories from FMEA or corrective actions
Pareto Is Not the Same as ABC Analysis
ABC inventory analysis uses annual consumption value to classify inventory into management groups. Pareto analysis is a broader prioritization method that can be applied to almost any measurable problem. ABC may display a Pareto-like concentration, but the two concepts should not be treated as identical.
Related: ABC vs VED/VEN Analysis and FMEA in Supply Chains.
Limits of the 80/20 Rule
- The ratio may be 70/30, 90/10 or something else.
- Frequency and financial impact may rank causes differently.
- A low-frequency event may still require priority if its safety or compliance consequence is severe.
- Pareto identifies concentration; it does not establish causation.
Interview Question
Question: If the top two defect categories represent 75% of defects, should you ignore the remaining 25%?
Answer: No. Pareto helps prioritize the first improvement effort. Lower-frequency categories may still have major safety, customer or compliance consequences and should be assessed separately.
