Now that we have talked about defining Six Sigma and 10 stupid Six Sigma tricks, I’ll move on to the measure phase and discuss some things that work and don’t work in measuring the effect of Six Sigma. The new metric that Six Sigma brought to us was the sigma index, so let’s start with it. Whenever I refer to this index, I will write out “sigma” and put scare quotes around it. This will get tiresome, but this is necessary to differentiate it from the statistical term for standard deviation. I’ll tell you up front that I’m not a big fan of the sigma index for a couple of reasons, which I promise I’ll get to.

But first, what is “sigma”?

This is a bit convoluted, I warn you.

A “sigma” by any other name . . .
Let’s say you have a process that produces output that’s measured on a continuous scale such as thickness or time. To make it easier, let’s assume that the process produces output that’s normally distributed and that the specification is symmetrical about the target.

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