Nelson / Westgard Rules available on P charts, but not. Laney P' charts

DHHaas — Fri, 05 Sep 2025 15:48:59 GMT

Hi -

I have noticed that in Control Chart Builder, JMP 18.2.1, if I create a P chart, JMP provides options for warnings for a number of different Nelson & Westgard rules. However, if I switch to Laney P', only "Test Beyond Limits" is an option. I'm curious if someone can explain the reasons why ... software bug? Good statistical reason those tests aren't applicable for a Laney P' chart? Something else entirely?

Thanks in advance.

Re: Nelson / Westgard Rules available on P charts, but not. Laney P' charts

jthi — Fri, 05 Sep 2025 15:59:01 GMT

At least it shouldn't be a bug as it is mentioned in the documentation:

Westgard Rules Quality and Process Methods > Control Chart Builder > Control Chart Builder Options > Options Panel and Right-Click Chart Options

(Available for Variables and Attribute chart types that are not Laney P′ or Laney U′ charts and for Short Run control charts.) Specifies the set of Westgard statistical control tests that are enabled. Because Westgard rules are based on sigma and not the zones, they can be computed without regard to constant sample size. For more information about tests, see Westgard Rules.

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Nelson / Westgard Rules available on P charts, but not. Laney P' charts

Re: Nelson / Westgard Rules available on P charts, but not. Laney P' charts