Six Questions about Six Sigma

Question 1:  What exactly is a sigma, (let alone six of them)?

It is a measure of how good a process is at delivering something that a customer wants.

Just because a customer wants it, it doesn’t necessarily mean that the process is capable of delivering it.  I might have wanted a son, think of the train sets and football, but two daughters later it becomes clear that my wife can’t produce them consistently.  (For those of you with an understanding of biology she can argue strongly it is my fault.)

Question 2:  So if my processes don’t vary I don’t need to worry about it?

All processes give variable outcomes:

  • The time it takes to drive to work varies
  • Two pairs of jeans may claim to be the same size but they fit differently
  • No two McDonald’s burgers look or taste exactly the same

Everything varies.  The question shouldn’t be “Does my process vary?” but  “Is this variation bad enough for a customer to get upset about it?”

Question 3:  Ok, so how good is a one sigma process then?

It messes things up about two thirds of the time, if I can second guess where the line of questioning is going:

  • One sigma: 2 defects in every 3 goes
  • Two sigma: 1 defect in every 3
  • Three sigma: 1 defect in every 15
  • Four sigma: 1 defect in every 161
  • Five sigma: 1 in every 4,348
  • Six sigma: 1 in every 294,117 (not very often)
It is a very steep scale.

Question 4:  Crikey if six sigma is so good what is all the fuss about?

It is probably not a good idea to get hung up about being six sigma.  I guess (but can’t prove) it is called six sigma because the phrase trips off the tongue nicely and a sigma looks surprisingly like a six that has fallen on its side.  The name is a marketing mans dream.  I wish I had thought of it, I would be very rich by now.

Question 5:  So do I ever need a six sigma process?

It depends on what you and your customers can  live with.  My wife doesn’t deliver sons to a two sigma standard, but I love my daughters  I am quite happy.  Would I get on a plane that wasn’t 6 sigma.  Erh, not knowingly, I will have a ten sigma one please.

Question 6:  So what do I need to remember?

  • All processes vary
  • Sometimes that upsets the customer
  • Upset customers are not good for business
  • Six sigma is simply a way of measuring how bad the variation is and some ways of doing something about it.

Oh, and if anybody tells you that all of their processes are six sigma they are talking out of the top of their hat.
Six Sigma

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Image by Canned Muffins


  1. Hi James,
    When it comes to quality management methods I’m slightly disdainful at some of the big promises that are made. Six Sigma is only one of many that have come along. I remember when ISO9000, otherwise known as BS5750, was introduced as the saviour of industry. However, may father summed it up in a nutshell when he said that no amount of quality management will guarantee that you make a product that your customer likes….after all garbage in, garbage out.

    By the way, why is your customer concerned about your internal processes? Shouldn’t they just be concerned about your output?


  2. Hi James

    A great way of explaining processes, variation and six sigma that does not require a stats background!

    I totally get the need to reduce variation so as toget the world to conform to our wishes. Yet, I wonder if there are domains of business, of life, where variation is simply what is so and so we have to build flexible / responsive means to act harmoniously with that variation. What is your thinking on this?



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