topic Re: ANOM JMP v's Wheeler in Discussions

ANOM JMP v's Wheeler

Gadsdon — Sat, 10 Jun 2023 23:21:11 GMT

Hi I am trying to replicate an ANOM that Wheeler did in Understanding Industrial Experimentation p60 (details attached)

I have attached the data set, I get different control limits for some reason, I set the alpha level at 0.10

Can you advise

Re: ANOM JMP v's Wheeler

KarenC — Sat, 24 Oct 2020 03:48:17 GMT

The JMP help notes that JMP implements the methods from Nelson, et. al (2003). link to JMP ANOM help

The methodology in the Nelson book differs slightly from Wheeler's, for instance the measure of error differs. Therefore, the ANOM decision limits calculated in JMP will differ from those in the Wheeler book. You can find the Nelson ANOM book here (ANOM Book ).

For the equal case for means the decision limits are:

Re: ANOM JMP v's Wheeler

Gadsdon — Sun, 25 Oct 2020 17:54:20 GMT

Thanks Karen, I asppreciate your response here

Re: ANOM JMP v's Wheeler

Gadsdon — Sun, 25 Oct 2020 17:59:43 GMT

Hi Karen, I just looked at the book, your one of the the authors. So which is the best method and why ;0)

Re: ANOM JMP v's Wheeler

KarenC — Mon, 26 Oct 2020 14:38:43 GMT

Wheeler uses ranges, JMP/Nelson uses standard deviations. Generally they are going to give you "similar" results. The key is plot your data, understand your measurement systems, use ANOM decision lines to guide your decision making. Since you are using JMP use the ANOM charts in JMP.

Re: ANOM JMP v's Wheeler

Gadsdon — Thu, 29 Oct 2020 16:21:15 GMT

Thanks, that really helps understanding the difference. I have dealt with SD and ranges with the control charts. The Shewhart chart and the Levey–Jennings charts for calculating control limits, where the Levey–Jennings uses SD. Its important to understand these differences.

Re: ANOM JMP v's Wheeler

Mark_Bailey — Fri, 30 Oct 2020 09:57:26 GMT

Another important distinction between Shewhart charts and Levey-Jennings charts is that the former types rely on short-term variation that is internally estimated in Phase I. The latter type often uses externally determined long-term variation. A clinical laboratory scenario, from which they originated, is given the SD or control limit information by the manufacturer of the assay, which they base on a precision study that intentionally includes long-term variation.

Re: ANOM JMP v's Wheeler

Gadsdon — Fri, 30 Oct 2020 14:37:44 GMT

Hi Mark

I must admit I do struggle with Levey-Jennings charts. When the process chart is stable the control limits equate to Shewhart chart limits, but when the process is not in control (as mesured by the Shewhart chart) the control limits are more forgiving (wider). Now I undertand that the Westguard Rules should then kick in, but very often people do not use these Rules, so the sensitivity of the Levey-Jennings chart is diminnished. A Strong signal becomes a Weak signal. The standard deviation component of the Levey-Jennings chart assumes the data is consistent, stable and attempts to fit these wider control limits to all the data.