Six Sigma–Testing the Process, not the Product


In the last post, I mentioned that the authors Ikel Harry, Ph.D., and Richard Schroeder of the book Six Sigma:  The Breakthrough Management Strategy Revolutionizing the World’s Top Corporation were extolling the value of metrics to be able to reveal the hidden cause “X” of the outcome “Y”.

I wanted to expand this basic concept of Six Sigma by mentioning that the outcome “Y” is what can be observed in the product, so that when you are inspecting a product, you are looking at outcome “Y”.   Obviously, if outcome “Y” contains defects, you want to get rid of them.   But you don’t focus on Six Sigma on changing “Y”.  What you do is you focus on the process “X” which is somehow causing “Y”.

Sometimes you have to go through a process of elimination, where you end up formulating hypothesis and hypothesis that posits a series of processes as the hidden culprit, only to find that changing them doesn’t make the defects in “Y” go away.  In that way, it’s like if you were in a sculpture class, and the instructor gave you a block of marble and said “carve a copy of this statue of an elephant.”   If you say “I don’t know how to carve an elephant,” he may say, “well, then take the block of marble and chip away everything that isn’t an elephant.”

In a sculpting class, that may not be practical advice, but in the Six Sigma world, proving hypotheses to be false (chipping away those parts that are not the problem) may end up revealing or hinting at those hypotheses that end up being true.

But you will only get to that correct hypothesis by focusing on the various processes that produce the product.   And that is why Six Sigma is said to test the process.    Since you cannot test a process directly, you have to test it indirectly by studying what effect changing it has on the visible product “Y”.

So it is an excellent tool for detection–but only if you first know where to look and what you are looking for!

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