The Key Principles of Six Sigma

Six Sigma is a complex topic which covers the whole process of eliminating defects from a process while simultaneously understanding and responding to the needs of the customers.

Six Sigma is a systematic approach used to improve products and processes through the reduction of variability. By relying on data, statistical analysis and proven process improvement techniques, Six Sigma provides a framework for companies to achieve a goal of as close to zero defects as possible.

In this article, the Fluere team explains:

  • What Six Sigma is,

  • What Six Sigma methodology is, and

  • What the process of implementing Six Sigma methodologies into your business looks like.

What is Six Sigma?

Sigma (σ) is a letter in the Greek alphabet. In statistics, the letter is used to represent the standard deviation of a population, a measure of how spread out the data points are, shown in the bell curve below. In Six Sigma methodology, sigma indicates one standard deviation level from the mean value of the process. Relating this to defective products means that the higher a sigma level of a process is, the fewer defects are created.

Standard deviation

Many companies state defect levels based on percentages and typically have anywhere between 5% to 30%. While this may intuitively sound good, out of one million products, that’s still 50,000 to 300,0000 defects – which corresponds to a 2 or 3 sigma level. Even a 1% defect rate still accepts 10,000 defects per million products!

Six Sigma methodology (along with other techniques from the process improvement toolbox), provides the to reach a much higher level of accuracy. A Six Sigma performing process will only produce 3.4 defects per million opportunities, almost a zero defect scenario.

A defect does not always have to be a physical product. In Six Sigma, a defect can be anything that does not meet the needs of the customer, such as a lead time that is too long or delivery performance is too varied.

In addition to reduce the acceptable number of defects, Six Sigma also places an emphasis on understanding the voice of the customer and eliminating the level of variation in your processes. As your Sigma level increases, your costs go down and your customer satisfaction increases.

The History of Six Sigma

The first advocate of Six Sigma was Motorola in the early 1980’s. Engineer Bill Smith introduced the idea and began structuring Motorola’s processes around its guidelines. Other major brands which fully embrace Six Sigma after its official formulation in 1986 were General Electric and Sony.

As time has gone on, more and more companies are adopting Six Sigma into their business rationale. Brands such as Vodafone, Axa, and Barclays have all recognised the value of Six Sigma.

Six Sigma Methodology


The most common methodology of Six Sigma is DMAIC (duh-may-ick), which is structured into five phases: Define, Measure, Analyse, Improve, and Control. This provides the step-by-step guide that businesses use to improve their processes. Below is a more in-depth look at what each phase entails:


The initial phase of the project involves clearly defining the problem and the desired outcomes. Understanding exactly what the symptoms of a problem are go a long way to identifying the root cause of the issue.


This stage is based around quantifying the problem defined in the first phase. In order to do this, quality of the product or process must be measured alongside production lead time and other variation in the process, depending on the goal. This measurement process gives a quantifiable reference point to base the projects progress on.


This is an investigation into the potential root cause of the problems based on the data previously collected. By identifying the sources of the issues that results in variation and defects, analysis can be done, often in several iterations, to determine the true root cause of the problem.


Once the true root cause of the problem has been identified, sustainable solutions can be developed to resolve them. During this stage, pilots of the solutions are tested to see if the improvement is viable and sustainable on a larger scale. Once improvements have been put in place, the progress against the initial readings taken in the measure phase can be monitored.


The final stage deals with the issue of sustainability in more detail. How will the improvements be continued beyond the implementation stage? Also, is there the possibility that any gains which have been made during the implementation stage will disappear over time? A plan can now be drawn up to monitor progress to ensure the process continually performs at the new improved level.

The DMAIC Roadmap

DMAIC Roadmap

The phases above are used in order, so a roadmap of a Six Sigma improvement process looks like this:

  1. The team is presented with a practical problem.

  2. This practical problem is then turned into a statistical problem after sufficient data has been gathered.

  3. Analysis is undertaken and a statistical solution is created as an answer to the statistical problem.

  4. The statistical solution is translated back into a practical solution to the initial issue.

  5. This solution is then trialled and fully implemented if effective.

Each individual case will have its own intricacies and challenges which need to be overcome. However this roadmap serves as the standard response to most problems that face businesses today.

Roles in Six Sigma

Six Sigma has a unique organisational structure in which every individual can attain a certain role.

Yellow Belt – These people are trained and made aware of basic Six Sigma tools and contribute their knowledge to Green Belt and Black Belt-led projects.

Green Belt - These people are trained in Lean Sigma tools and are capable of completing smaller-scale projects by themselves. They can also apply the DMAIC framework.

Black Belt – These people can lead and manage cross functional projects as well as completing advanced statistical analysis and educating others.

Master Black Belt – These people are full-time leaders, coaches, and mentors. They specialise in teaching people how to effectively apply DMAIC to resolve problems.

Sponsor – These are senior leaders within companies who are looking to embed Six Sigma methodologies into their processes. Their responsibilities involve gaining support from the Six Sigma community to balance their customer, business, and people requirements.


Improve your manufacturing company’s processes with Fluere

To reduce the number of defects in your operation, get in touch with one of our Process Improvement Consultants. Are you thinking of, or already performing, a Six Sigma improvement programme? Get in touch with us to find out how we can offer Transformational Support to help you and your business.

Call us on: 0113 250 6768 to find out more about how we can help you.

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