Great book by Donald Wheeler. I’m over a year late to this SPC discussion, but SPC charts would be much less powerful if they had been based on the overall calculated stdev() instead of what might be called an approximation for standard deviation. SPC works because it uses somewhat less efficient but much more robust estimators for a normal distribution’s sigma at the local data scale instead of the most efficient but brittle global estimator stdev().

The recent post on SPC Approach to Browser Stats shows a nice example of how much better SPC does because of its robust estimators. StDev() includes the variation due to a trend line and makes for much less convincing charts, but SPC sigma ignores almost all of that special cause, giving SPC charts the power to clearly detect the special cause.

As the underlying distribution becomes decidedly non-normal, I or I-MR charts stop working so well, and Xm-R charts (perhaps with increasingly large subgroups) are needed to take advantage of the central limit theorem and normalize the variable being plotted. (None of the controversy about whether to show the MR charts or not has anything to do with how the I chart limits are calculated — it’s still based on an average moving range, or a median moving range if even more robustness against outliers is desired.)

You pretty much have to do your own macro, since your configuration will be unique. Here are a couple of articles which may help:

How To: Record Your Own Macro
How To: Fix a Recorded Macro
How To: Assign a Macro to a Button or Shape

Darlene

This is an issue with pivot charts, in every version of Excel that has pivot charts (2000 and later). In Changing a PivotChart removes series formatting in Excel Microsoft admits it’s an issue, and their suggestion is to record a macro next time you have to fix the chart. Thereafter, all you need to do is run the macro when necessary.

Thanking you in advance for your expertise.

Darlene