The 80/20 rule in Six Sigma is known as the Pareto Principle.
It states that about 80% of problems come from 20% of causes.
It helps identify the most important issues for process improvement.
What is the 80 20 rule in Six Sigma?
The 80/20 rule used in Six Sigma refers to the Pareto Principle: roughly 80% of problems come from 20% of causes.
In Six Sigma, it helps teams focus on the few critical causes (“vital few”) instead of the many less important ones (“trivial many”).
Example in electroplating:
Suppose a factory records 1,000 defects:
- 450 → coating thickness variation
- 250 → poor adhesion
- 150 → pitting
- 100 → burns
- 50 → discoloration
You may find that:
- Coating variation + poor adhesion = 700 defects
- These 2 causes are only 2 out of 5 causes (40%), yet they create 70% of defects
That’s close to the 80/20 concept: a small number of causes create most of the impact.
Six Sigma teams often use a Pareto chart during the Analyze phase of the DMAIC process:
- Define → identify problem
- Measure → collect data
- Analyze → use Pareto to identify major causes
- Improve → fix those few major causes
- Control → sustain improvements
Why it matters:
- Saves time and money
- Prevents solving low-impact issues
- Helps prioritize improvement projects
- Drives larger gains with focused effort
The 80/20 ratio is not an exact law. Sometimes it might be 70/30, 90/10, or 95/5—the principle is simply that a small number of causes usually create most of the results.
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