What is Six Sigma?
Six Sigma is a data-driven quality management methodology that aims to reduce process variation and defects to near-perfection—3.4 defects per million opportunities. It uses the DMAIC framework (Define, Measure, Analyze, Improve, Control) to systematically identify root causes of quality problems and implement sustainable solutions.
Six Sigma was pioneered by Motorola in the 1980s and popularized by GE under Jack Welch. The methodology is grounded in statistical analysis—"sigma" refers to standard deviations from the mean, and six sigma represents a process that is 99.99966% defect-free. Practitioners are certified in a belt system: Yellow Belt (basics), Green Belt (project team member), Black Belt (project leader), and Master Black Belt (program leader).
The DMAIC framework provides a structured approach: Define the problem and customer requirements; Measure current performance and collect data; Analyze data to identify root causes; Improve the process by implementing solutions; Control the improved process to sustain gains. Each phase has specific tools—from voice of the customer in Define to statistical process control charts in Control.
In case interviews, Six Sigma concepts are relevant for quality improvement and operational efficiency cases. While you won't be expected to perform statistical analysis, understanding the DMAIC framework and the concept of reducing variation demonstrates operational acumen. Six Sigma is often combined with lean manufacturing in "Lean Six Sigma."
Real-world example
GE saved over $12B in the first five years of its Six Sigma program. One notable project reduced aircraft engine blade defects from 25,000 per million to under 4 per million, dramatically improving reliability and reducing warranty costs.
Related terms
Lean Manufacturing
Lean manufacturing is a production methodology focused on minimizing waste within a manufacturing sy…
Total Quality Management
Total Quality Management (TQM) is an organization-wide approach to continuous quality improvement in…
Bottleneck Analysis
Bottleneck analysis identifies the constraining step in a process that limits overall throughput and…
Benchmarking
Benchmarking is the process of comparing a company's performance metrics, processes, or practices ag…
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