Six Sigma: why (and how) to use this methodology

4 minutes

In the world of quality and continuous improvement the term Six Sigma is often used. True to my objective of deciphering, I present you the method, step by step and tell you in which cases it is the more effective.

Six Sigma Principle

Formalized by Bill Smith (Motorola) in the late 1980s, the Six Sigma methodology combines several quality tools.

This methodology aims to improve processes in two ways:

  • reduce variability
  • increase accuracy.

If I use it for archery, the methodology will help the archer send all his arrows in the same place (variability) and in the center of the target (accuracy).

Two archery targets. One with a few scattered arrows, the other with several arrows close but not centered. Illustration of the SIx Sigma principle of variability and accuracy.

Its name corresponds to the target standard deviation: +/-6σ. The process will produce a result whose dispersion will be within an interval of six times the standard deviation of the target.

It uses various statistical tools to achieve and maintain improvements: AMDEC, SIPOC,variance analysis, DoE, Statistical Process Control, to name a few.

Six Sigma at its best

The main advantage of this methodology is its rigour. Using mathematics and statistics, it is perfect in critical environments. I am thinking of the aeronautics, food, pharmacy, but also healthsectors.

If you work in an environment with people who pay great attention to details such as accountants or scientists, it will help you work with them.

Finally, if you produce standard goods or services, the Six Sigma methodology can help. By standard, I think of a spatial or temporal identical dimension. For example, the length of a piece, or its diameter, a call time lenght or a processing time.

Apply DMAIC step by step

DMAwhat? Pronounced dah-MAY-ik, this acronym describes the steps of the Six Sigma methodology:

  • Define
  • Measure
  • Analyse
  • Improve
  • Control

Like any methodology, it follows the four stages of the Deming Wheel (Plan Do Check Act),focusing on the second part: Do. It helps to be rigorous in the implementation of the plan.


In Phase 1, the team will organize and identify the problem to be solved. To do this, it will use the traditional tools of project management and problem identification: brainstorming, root cause analysis, …


Then comes the time of measurement, it is phase 2. This is the critical step for succeess in the project. It consists of gathering information, preferably quantitative on the process and what can impact it. Gathering information must be comprehensive and fair. Otherwise, the next step, analyze, will produce poor results. This is the too famous “garbage in, garbage out”, which means that the result cannot be better than the input data.


Phase 3 is the one that will help you satisfy the regulatory authorities, extreme quality requirements and number afficionados. Without forgetting your bias and the difference between correlation and causality, you will analyze your data to get the best insights. Does the room temperature have a link with the length of the parts or the talk time?


With your analysis, you can then improve (phase 4), based on evidence. It is at this stage that you decide the solutions and put them in place.


Finally, the phase 5 is to monitor, preferably continuously, the results. You confirm your assumptions were correct. Above all, you rely on the data and analysis to predict when the process begins to deviate and risk to produce unacceptable products or services.

And that’s it, it’s time to move on to another Six Sigma project. Given the collection of data and analysis, it takes between six and eighteen months to to carry out such a project. We are far from a quick gain, but it is a gain that will last in time.

To remember

In an approach of operational excellence, we often start by picking low hanging fruits, with simpler tools or approaches. Then, to continue the improvements, other methodologies and tools must be used. Six Sigma is one of them, which has proven its worth.

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