Six Sigma
Definition
Six Sigma is a disciplined, data-driven methodology for eliminating defects and reducing variation in any process, targeting performance at 3.4 defects per million opportunities — statistically, six standard deviations from the mean.
Motorola engineer Bill Smith developed Six Sigma in the 1980s; Motorola won the Malcolm Baldrige National Quality Award in 1988 using it. Jack Welch made Six Sigma central to GE's strategy in the 1990s, turning it into the dominant quality methodology of the era.
'Six sigma' refers to the statistical target. In a normal distribution, six standard deviations (sigma) on each side of the mean captures 99.99966% of outcomes — leaving only 3.4 defects per million opportunities. Most processes operate at three to four sigma (roughly 6,000 to 67,000 defects per million), so reaching six sigma is a significant step change.
Six Sigma has two primary methodologies:
- DMAIC (Define, Measure, Analyze, Improve, Control) — for improving existing processes
- DMADV (Define, Measure, Analyze, Design, Verify) — for designing new processes or products from scratch
Practitioners are certified at different levels: Yellow Belt (basic), Green Belt (project leader), Black Belt (full-time improvement professional), and Master Black Belt (organization-wide leader and trainer).
Six Sigma tools include control charts, fishbone (Ishikawa) diagrams, Pareto charts, process capability analysis, hypothesis testing, and design of experiments. Many of these get drawn on whiteboards during project kickoffs and analysis sessions.
Examples
- Manufacturing: reduce injection-molded part defect rate from 4,000 per million to under 100 per million using DMAIC
- Healthcare: reduce medication dispensing errors from 2% to 0.001% using Six Sigma process redesign
- Financial services: reduce loan processing errors and rework by mapping the process and eliminating non-standard steps
- Software: apply Six Sigma to deployment failure rates — measure current failure rate, analyze root causes, improve CI/CD pipeline, control via monitoring
Related terms
Snap a six sigma. Ship its actions.
BoardSnap turns any whiteboard — including this one — into a summary and action plan.