nav[aria-label="Primary Navigation"] { padding: 0; & ul { list-style: none; width: 100%; display: flex; flex-direction: row; justify-content: start; align-items: start; gap: 30px; padding: 0; & li { margin: 0; } & ul li { list-style: none; } } }

question about _Std Dev on limits table created by control chart platform

antonio-domenic

Can anyone tell me what is the _Std Dev value in the table that is created using the command Save Limits in New Table of control chart platform? I suppose it is the standard deviation of the dataset, but the value I see is different from the value that is calculated, for example, using the Table Summary Std Dev. I verified that using different datasets, JMP 15.1, JMP13. Is there anything that i misunderstand?

Accepted answers

txnelson

The _StdDev value is the mean of each of the subgroup's standard deviations.

All comments

txnelson

The _StdDev value is the mean of each of the subgroup's standard deviations.

antonio-domenic

Make sense! Thanks a lot!

Mark_Bailey

Your question is about the most basic aspect of a control chart: the estimation of the short-term process variability in the absence of a special cause (in control state). Your question suggests that you have not learned about the purpose and construction of a control chart. While the control chart is 'just' a run chart with limits representing the natural variation, its simplicity does not mean that 'just' anyone can use it properly. I recommend that you start learning by reading the relevant chapters from Help > JMP Documentation Library > Quality and Process guide. Then seek one of the books by Doug Montgomery or Don Wheeler, to name a couple of experts.

If you are charting important data to make important decisions then learning about proper control chart analysis is worth your time.