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Six Sigma – Reducing Defects

Six Sigma
Six Sigma
Six Sigma

In the world of quality, Six Sigma is one of the biggest names. Total Quality Management (TQM) may aim for zero defects. But Six Sigma aims to reduce defects down to a statistical blip – arguably a more realistic enterprise.

What makes Six Sigma such a compelling proposition is the vast asset base of tools and process that accompany the core idea. What makes it a big idea is the impact it has had on manufacturing, combined with its wider potential in other domains.

Why ‘Six Sigma’?

The term ‘Six Sigma’ can easily sound like just one more meaningless brand name. But it is far from that.  In fact, it’s a precise description of the big idea at the core of the methodology.

In statistics, the commonest measure of deviation from the mean – or ‘norm’ – is the standard deviation. So, the more homogenous a population is, the smaller the standard deviation. Statisticians use the Greek letter sigma (σ) to denote standard deviation.

If you take any aspect of a part that a factory manufactures, and measure it, you would expect the mean measurement to match the design specification. All that Six Sigma does is reduce the number of defective parts to six standard deviations. This works out at fewer than four per million units produced. For technical reasons, this error rate is actually calculated from a 4.5σ deviation from a mean shifted 1.5σ from the desired mean. Don’t ask me what those technical reasons are.

What is Six Sigma?

When Motorola introduced the idea of Six Sigma as a means to reduce defects, it was a purely defensive tactic. They wanted to match the quality standards their competitors were able to achieve. Six Sigma was a metric for a quality standard.

Now, it is much more. You can view Six Sigma as a:

  • methodology for achieving quality
  • management approach that dominates the company’s ethos
  • toolset for business improvement
  • basis for a huge consulting and training business

However, it is important to understand that Six Sigma does not seek to overhaul the operating model and processes of a business. Rather,  it imposes performance improvement processes on top of existing processes. It is far less radical than business process re-engineering (BPR), for example.

The Benefits of Six Sigma

The primary benefits are:

  • Improved quality
  • Reduced waste
  • And therefore reduced cost
  • And increased customer satisfaction

Training for Six Sigma

Six Sigma training uses the metaphor of coloured belts, lifted from Japanese martial arts.

  • Yellow Belt
    Typically one to two weeks’ training to learn to use the basic tools of Six Sigma.
  • Green Belt
    Typically two to three weeks’ additional training, to handle problem-solving tasks, leading small teams. Green belts often do much of the work on a Six Sigma initiative.
  • Black Belt
    Typically an additional two to four weeks’ training, the experience of two or more Six Sigma projects, and passing a test will bring you to black belt status, where you can lead your own team.
  • Master Black Belt
    With lots of experience and lots of training, you can train, mentor and advise black belts.

A Peerless Toolset

Only the Toyota Production System (TPS) can boast a comparable toolset of business performance improvement tools. We’ve covered many of them in earlier Pocketblogs:


Double the Goodness

One of the jewels of the Toyota Production System is Lean Manufacturing. What if you could cross this with Six Sigma, to create Lean Six Sigma? Well, guess what? It’s a thing. While Lean manufacturing focuses on efficiency, speed, and eliminating waste, we can combine pace and cost performance with quality performance: optimising the whole time, cost, quality triangle. Faster, cheaper and better!

This is now a popular approach, not just in manufacturing, but in financial services, transportation, retail, and even Government.

What is Your experience of Six Sigma?

We’d love to hear your experiences, ideas, and questions. Please leave them in the comments below.

To learn more…

We have written a fair number of articles about quality and quality management. I’d especially recommend:

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