Six Sigma Metrics
Six Sigma is a data-driven approach to process improvement that aims to reduce defects to near-zero levels. DPMO (Defects Per Million Opportunities) is a key metric that quantifies process performance and helps determine the Sigma Level.
Where:
- Defects = Total number of defects found
- Units = Total number of units produced
- Opportunities = Number of potential defect opportunities per unit
Six Sigma Results
DPMO
Defects Per Million Opportunities
Sigma Level
Process Capability
Yield
Percent Defect-Free
Sigma Scale
Interpretation
Six Sigma Benchmarking
| Sigma Level | DPMO | Yield | Quality Level |
|---|---|---|---|
| 1σ | 691,462 | 30.85% | Unacceptable |
| 2σ | 308,538 | 69.15% | Marginal |
| 3σ | 66,807 | 93.32% | Average |
| 4σ | 6,210 | 99.38% | Good |
| 5σ | 233 | 99.98% | Excellent |
| 6σ | 3.4 | 99.99966% | World Class |
Practical Examples
Example 1: Manufacturing Process
Units: 1,000 | Defects: 45 | Opportunities: 2
DPMO = (45 / (1,000 × 2)) × 1,000,000 = 22,500
Sigma Level ≈ 3.5σ (Between 3σ and 4σ)
Example 2: Service Process
Units: 500 | Defects: 6 | Opportunities: 5
DPMO = (6 / (500 × 5)) × 1,000,000 = 2,400
Sigma Level ≈ 4.3σ (Between 4σ and 5σ)
Example 3: High-Quality Process
Units: 10,000 | Defects: 3 | Opportunities: 1
DPMO = (3 / (10,000 × 1)) × 1,000,000 = 300
Sigma Level ≈ 4.8σ (Approaching 5σ)
Understanding DPMO and Sigma Level
DPMO provides a standardized way to compare processes with different complexities. The Sigma Level translates DPMO into a simple scale from 1 to 6 (or higher), where higher values indicate better process performance.
Most organizations operate at 3-4 Sigma levels. Six Sigma performance (3.4 DPMO) represents near-perfect processes, with only 3.4 defects per million opportunities.
Using these metrics helps organizations:
- Benchmark process performance against industry standards
- Identify improvement opportunities
- Set quality improvement targets
- Measure the impact of process changes