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The Six Sigma Summary

I recently completed the Six Sigma Black Belt Certification. So here is a set of collected notes that summarise what it is and how to put it into practice. Hopefully, this will clear a lot of doubts about Six Sigma and allow budding Program Managers to understand the concepts without having to read too many books and material out there!

To apply Six Sigma to your business and produce the best results, you need to understand what Six Sigma is, the principles of Six Sigma, and the DMAIC problem-solving method. The correct tools and use of the Six Sigma scale and methods will keep your data dependable and reusable.

What Is Six Sigma?

Generally, Six Sigma is a problem-solving methodology that helps enhance business and organisational operations. It can also be defined in a number of other ways: 

  • A quality level of 3.4 defects per million opportunities
  • A rate of improvement of 70 percent or better
  • A data-driven, problem-solving methodology of Define-Measure-Analyse-Improve-Control
  • An initiative taken on by organisations to create bottom-line breakthrough change

Six Sigma Principles

Six Sigma is based on a handful of basic principles, and these principles create the entire Six Sigma arrangement. Here are Six Sigma's fundamental principles:

  • Y=f(X) + ε: All outcomes and results (the Y) are determined by inputs (the X's) with some degree of uncertainty (å).
  • To change or improve results (the Y), you have to focus on the inputs (the X's), modify them, and control them.
  • Variation is everywhere, and it degrades consistent, good performance. Your job is to find it and minimise it!
  • Valid measurements and data are required foundations for consistent, breakthrough improvement.
  • Only a critical few inputs have significant effect on the output. Concentrate on the critical few.
  • Every decision and conclusion has risk (ε), which must be weighed against the context of the decision.

The Six Sigma Scale

 The Six Sigma scale shows how well a vital feature performs compared to its requirements. The higher the sigma score, the more efficient the feature is. This table shows the universal Six Sigma scale:

Sigma Level (Z)

Defects per Million Opportunities (DPMO)

Percent Defects (%)

Percent Success (Yield %)

Capability (CP)
































The DMAIC Method of Six Sigma

The DMAIC (Define-Measure-Analyse-Improve-Control) project method is a formalised problem-solving process of Six Sigma. It's made-up of five steps to apply to any procedure of a business to improve effectiveness.

  1. Define: Set the context and objectives for your improvement project.
  2. Measure: Determine the baseline performance and capability of the process or system you're improving.
  3. Analyse: Use data and tools to understand the cause-and-effect relationships in your process or system.
  4. Improve: Develop the modifications that lead to a validated improvement in your process or system.
  5. Control: Establish plans and procedures to ensure that your improvements are sustained.

The Tools-Methods Landscape of Six Sigma

Having the right tools and knowing how to apply them to your Six Sigma projects will help you produce accurate, acceptable, and reusable outcomes. Here's an overview of the Six Sigma landscape:


DMAIC (Define – Measure – Analyse – Improve – Control)


As seen above, The Six Sigma Methodology uses the DMAIC approach.  It is a five-step approach that drives unwanted variation from products and processes. By understanding and controlling underlying root causes, teams fix problems at the source, resulting in the lowest possible cost of quality for a given process.

It's no wonder that so many feel like lost when it comes to Six Sigma: every significant process improvement tool developed over the years has been placed under the Six Sigma umbrella, along with a healthy dose of statistics. But the good news is that most processes can be improved with a well-defined problem, the right team, and a simple set of process improvement tools. So the Pareto Principle applies to the Six Sigma toolkit itself: a small handful of process improvement tools (which existed long before the Six Sigma approach was created) will solve the majority of the problems that a team will encounter – tools involving very little in the way of statistics. Too many Six Sigma practitioners and consultants make Six Sigma about the tools, and not about the results. Stay focused on results and learning the best methods to achieve those results, and you will become a "designated-hitter" in your organisation.

So what are the key ingredients and tools that will solve the majority (let's say 4 out of every 5) of process improvement challenges?

  • A clearly defined problem statement that is narrow enough in scope for the team to succeed.
  • Data to support where the process is currently, in terms of defects per million, scrap cost, sigma-level, or whatever measure is going to be improved upon.
  • A project team made up of those who understand the process the most, and a team leader who is respected, understands the basics of DMAIC, and can keep the team on track.
  • Positive management support – team members will need time to collect data and work on the project.

If the above ingredients are in place, the team has an excellent chance of succeeding. Now for some specific tools to deploy during the problem solving process –

  • Develop a flow-chart of the current process.
  • Develop a fact-based Pareto Chart.
  • Conduct a 5-why analysis that addresses the significant Pareto items.
  • Brainstorm and verify possible solutions – in many cases, those closest to the process (those working with it every day – make sure they are part of the team) know what needs to be done – oftentimes a Six Sigma project simply brings the necessary focus to implement long-overdue fixes.
  • Implement the fixes.
  • Verify that the fixes have improved the process.
  • Implement controls, audits, etc., where necessary to ensure the fixes are sustained over the long run.

That's it. The remaining 20% of the problems might need more advanced methods inside the DMAIC toolkit.  Understanding those tools will place you in the top 1% of all problem solvers.

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