Do you still insist on asking, “Which chart do I use for which situation?”

I’ve seen many flowcharts in books to help you answer this question. They’re all some variation of this:

I find them far too confusing for the average user and have never taught this in my work. Besides, you get no credit for choosing the technically correct chart or computing the right numbers—only for taking the right action.

Your ‘Swiss Army knife’

For any initial chart for process assessment, the data should be in its naturally occurring time sequence, preferably as a run chart. Next, the control chart of choice with which to start is virtually almost always the I-chart (individuals chart), which uses the moving range (MR) between consecutive points to determine its common-cause limits. The I-chart is the “Swiss Army knife” of control charts. As I have discovered time and time again, it usually approximates the “correct” chart under most conditions, and its use is easier to explain.

I can hear the chorus: “So, what are the conditions when it isn’t correct?”

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