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What is Six Sigma?

If your wondering "What is Six Sigma" you've come to the right place. Black Belts and Master Black Belts across the globe struggle answering this question. The fact is, it's not a simple answer.

It's great when the one inquiring has some general understanding of process, process performance and statistics, they are more prepared to grasp the real answer which you'll read about shortly. In the end however, most simply describe it as a business and process improvement methodology which is a completely valid response but usually leaves those asking the question thirsting for more. So here's more...

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What is Six Sigma? it's a quality and process improvement program that follows a rigorous methodology referred to as DMAIC.

This acronym simply references the following 5 steps or phases of the six sigma approach

  • Define
  • Measure
  • Analyze
  • Improve
  • Control

This Black Belt training curriculum will explore all five phases in great detail.  You will learn the process, concepts and tools to become an expert in problem solving using the six sigma methodology.

Six Sigma refers to the Greek letter s which is commonly used to mean standard deviation.  The six (6) refers to the number of standard deviations on either side of the mean of a process performance measure.

If a process performs such that the average output of the process is 6 standard deviations away from the customers specification limit then the process is known to be a six sigma process which yields only 3.4 defects per million opportunities.

Average is +/- 6 stdev from customers upper & lower specs

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So what is Six Sigma or what is a Six Sigma process? It's one with a defect rate of 3.4 defects per million opportunities and has a performance yield of 99.99967%.  Impressive eh? Let's examine a process with a sigma level of only 3. 

A process operating at a 3 sigma level has a yield of 99.73% still sounds pretty darned good.  However, if many of the processes and services you use on a daily basis operated at 3 sigma, you (and many others) would be pretty unhappy customers…

Here are some effects of operating at 3 sigma or 99.73% (following data provided by

  • Virtually no modern computer would function.
  • 10,800,000 health care claims would be mishandled each year.
  • 18,900 US Savings bonds would be lost every month.
  • 54,000 checks would be lost each night by a single large bank.
  • 4,050 invoices would be sent out incorrectly each month by a modest-sized telecommunications company.
  • 540,000 erroneous call details would be recorded each day from a regional telecommunications company.
  • 270,000,000 (270 million) erroneous credit card transactions would be recorded each year in the United States.

I'm sure you agree that these levels of effectiveness are not even remotely good enough.  Functioning at 3 sigma or 99.73% sounds good but when it comes to things we all care about, services we come to expect, products we demand performance from, 99.73% is simply just not good enough.

Here are a few more examples of processes, products or services operating at 99%…

  • 20,000 lost articles of mail per hour.
  • Unsafe drinking water almost 15 minutes per day.
  • 5,000 incorrect surgical operations per week.
  • Short or long landings at most major airports each day.
  • 200,000 wrong drug prescriptions each year.
  • No electricity for almost 7 hours per month.

It's clear that there are examples of processes operating at levels far greater than Six Sigma on a daily basis.  It's also clear that for many things, functioning at 99.73% is not good enough. 

When companies turn to their own processes and services to evaluate their performance the difference might not be "dead people" but it can be lost income opportunities and huge cost burdens as a result of poor quality or only being 99.7% good.  These burdens require their attention if they intend to compete in today's economy.

What is six sigma? It's a goal, an aspiration to be 99.99967% Good at what you do!

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