The discipline
Six Sigma is a data-driven discipline for finding — and permanently removing — the causes of defects, until a process delivers near-perfect results as a matter of routine.
First principles
Six Sigma is a structured method for improving any process — machining a part, approving a loan, admitting a patient — by attacking the two things customers never forgive: defects and unpredictability. It replaces opinion with measurement, intuition with analysis, and one-off fixes with controls that make improvement permanent.
The name is a statistical promise. Sigma (σ) is the symbol for standard deviation — a measure of how much a process varies. A process “operating at six sigma” keeps so much distance between its natural variation and the customer’s limits that only 3.4 defects escape per million opportunities. That is 99.99966% right — not perfection, but close enough that customers stop noticing anything except quality.
Most organizations run at three to four sigma — thousands of defects per million, each one costing rework, refunds and goodwill. That gap is why employers pay for this skill: a certified practitioner can walk into a familiar mess, find its causes with data, and close it in a way that survives an executive’s scrutiny — and a customer’s.
The sigma scale
What each sigma level allows
| Sigma level | Defects / million | Yield |
|---|---|---|
| 1σ | 691,462 | 30.9% |
| 2σ | 308,538 | 69.1% |
| 3σ | 66,807 | 93.3% |
| 4σ | 6,210 | 99.38% |
| 5σ | 233 | 99.977% |
| 6σ | 3.4 | 99.99966% |
Defect rates follow the industry convention of a 1.5σ long-term shift — the same convention every major certification body uses.
Four decades of results
Six Sigma earned its reputation the hard way — by producing measurable results at some of the most demanding companies in the world, then proving it could do the same anywhere work follows a process.
1986
Facing competitors whose products simply failed less, Motorola engineer Bill Smith and his colleagues set a radical target: count defects per million instead of per thousand, and engineer every process toward near-perfection. The company called the initiative Six Sigma — and two years later won the first Malcolm Baldrige National Quality Award.
1995
Jack Welch made Six Sigma the centerpiece of General Electric’s strategy — training tens of thousands of employees, tying promotion to belt certification, and crediting the program with billions of dollars in savings. GE proved the method worked far beyond the factory floor, in businesses from jet engines to consumer finance.
2000s
Hospitals used it to cut medication errors, banks to speed loan approvals, airlines to turn aircraft around faster, governments to clear backlogs. As adoption spread, belt certification became hiring shorthand for a rare skill: improving a process with evidence instead of opinion.
Today
Modern practice blends Six Sigma’s statistical rigor with Lean’s relentless focus on speed and flow. The combined discipline — Lean Six Sigma — is now the default operating system of operational excellence, and the foundation of every program we teach.
The engine
Every Six Sigma project follows the same roadmap. Each phase answers one question, ends with a formal review, and hands verified conclusions to the next — so by Control, nobody is guessing.
Phase 1 of 5
“What problem are we solving, and why does it matter?”
The team turns a vague complaint into a chartered project: a measurable problem statement, a scoped process, named stakeholders, and a clear line to what the customer calls quality. A project that survives Define has already avoided the most common failure in improvement work — solving the wrong problem well.
Key tools
Phase 2 of 5
“How is the process actually performing today?”
Before anything changes, the team establishes the baseline — and proves the numbers can be trusted. That means precise operational definitions, a data collection plan, and a Gage R&R study to confirm the measurement system itself is not the problem. The phase ends with the current performance stated in hard numbers: a capability, a sigma level, a cost.
Key tools
Phase 3 of 5
“What is really causing the problem?”
Candidate causes come from the team’s experience — fishbone diagrams, the 5 Whys — but none survives on opinion. Each is tested against data with Pareto charts, graphical analysis and formal hypothesis tests, until the team can prove which few causes drive most of the defects. Everything downstream depends on getting this phase right.
Key tools
Phase 4 of 5
“What change removes the cause — and how do we know?”
The team generates solutions, selects against impact and effort, and pilots before committing. FMEA hunts down the ways a fix could fail before it does; a pilot or designed experiment proves the fix works on real work; mistake-proofing makes the right way the easy way. Only then does the change roll out.
Key tools
Phase 5 of 5
“How do we make sure the gains hold?”
Improvements decay unless they are engineered not to. Control charts watch the process for drift, a control plan spells out exactly who responds to what and how, and standard work makes the new method the default. Then the process is handed back to its owner — better, documented, and monitored.
Key tools
The belt ladder
Six Sigma borrows its ranks from martial arts: each belt marks a deeper command of the method and a bigger role on the project.
At the very top of the ladder, industry also recognizes Master Black Belts — the veterans who train Black Belts and steer an entire improvement program. Our programs at Averon Institute cover the four ranks employers ask for by name: White, Yellow, Green and Black.
White Belt gives you the vocabulary and the map. Yellow Belt adds a working toolkit for contributing to project teams. Green Belt makes you the person who leads improvement projects alongside a day job. Black Belt makes improvement the job — advanced statistics, program leadership, and the coaching of Green Belts. Here they are, side by side:
| Attribute | White Belt Foundation · Free | Yellow Belt Team Member | Green Belt Practitioner · Most popular | Black Belt Expert · Most advanced |
|---|---|---|---|---|
| Best for | A fast, credible first credential — proof you speak the language | Team members who want a hands-on toolkit, not just the vocabulary | Professionals ready to lead improvement projects at work | Experts who will run the improvement program itself |
| Time investment | 6 hours of material · most students finish within a week | 14 hours of material · typically 1–2 weeks part-time | 35 hours of material · typically 4–8 weeks part-time | 60 hours of material · typically 8–12 weeks part-time |
| Statistics depth | Concepts and vocabulary only — no formulas required | Practical basics — Pareto charts, check sheets, reading control charts | Applied — hypothesis tests, regression, control charts | Advanced — DOE, multiple regression, non-parametric methods |
| Project leadership | Contribute confidently as a project team member | Be the strongest contributor on a project team | Scope, charter and lead DMAIC projects end to end | Lead cross-functional programs and coach Green Belts |
| Exam length | 30 questions · 45 minutes | 50 questions · 60 minutes | 100 questions · 180 minutes | 150 questions · 240 minutes |
| Price | Free$99no card required, everything included | $129$219one-time, everything included | $299$449one-time, everything included | $499$749one-time, everything included |
| EnrollView White Belt | EnrollView Yellow Belt | EnrollView Green Belt | EnrollView Black Belt |
Every price is one-time and includes the proctored exam, one free retake, your certificate and lifetime access — backed by a 30-day money-back guarantee.
Two schools
They grew up in different factories solving different problems — and modern practice needs them both.
Lean
“Where does time, effort or material go to waste?”
Born in Toyota’s production system, Lean maps how value moves to the customer and strips out everything that slows it down.
Six Sigma
“Why does the process go wrong when it does?”
Born at Motorola, Six Sigma measures variation, proves root causes with statistics, and installs controls so the fix holds.
The synthesis
In practice the argument is over: mature organizations run both under one banner. Lean sets the pace and clears the path; Six Sigma proves the cause and locks in the gain. Our Green Belt and Black Belt programs teach Lean methods inside the DMAIC frame — because that is how the discipline is actually practiced today.
The next step
You know what Six Sigma is. Now become the person who practices it — self-paced, fully online, with a credential anyone can verify.
30-day money-back guarantee · See refund policy