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Primed SPC charts

It would be very beneficial to have the ability to select p' and u' SPC charts in the control chart utility. Especially in this day and age of big data which often times equates to BIG denominators. Our company has a vast number of use cases for "primed" charts and very few options out there in the software realm.

Defect ID:

Community Manager

@JosephRotford wrote:

It would be very beneficial to have the ability to select p' and u' SPC charts in the .

It looks like you've left out the object of the preposition here. Can you edit the idea and add the context?

Thanks!

Level II

@Jeff_Perkinson fixed!

Staff

Hey!  This is a good idea for a future feature in the Control Chart Builder platform.

The p-chart platform in JMP has a default 3 sigma set in the launch dialog. In certain cases sigma of 3 is too restrictive and larger values of sigma are prefered. The p'-chart is used for cases where the proportion of defects is low, because the denominator is very large relative to the number of defects, the control limits become very narrow and everything is out of control. The p'-charts have scaled control limits, Instead of assuming sigma =1 (KSigma=3) it is calculated from the data. This chart type uses a larger value that comes from an estimate of Sigma z, which results in wider control limits.

About 4 or 5 years ago I wrote a very basic script, to do the z sigma calculation and make a chart. Then I had to update the scritp because something broke. It works but I keep getting asked to add features, like a by role or other little tweaks and options (all of which make perfect sense, but take time to implement.)

I would love to see p' and u' charts as an option in the Control Chart Platform

https://community.jmp.com/t5/JMP-Scripts/Example-p-prime-chart-script-Constructing-p-charts-or-Laney...

Staff

I agree Byron!  It would be great to see these in JMP.

Staff

Have used the JMP p-prime chart script contributed by Byron Wingerd and found it to be very helpful!

Example-p-prime-chart-script by Byron Wingerd

Staff

Hi Scott and Byron - in my consulting days, we only rarely found situations in which p (or u) charts actually worked. There is almost always over or under-dispersion, rendering the p charts practically useless.

Level IV

Sounds like a great option!

@Byron_JMP  where the proportion of defects is low, because the denominator is very large relative to the number of defects, the control limits become very narrow and everything is out of control. The p'-charts have scaled control limits, Instead of assuming sigma =1 (KSigma=3) it is calculated from the data. This chart type uses a larger value that comes from an estimate of Sigma z, which results in wider control limits.

It reminds me of the case study - where in that case it was variable data and the X-bar & R Chart - in the STIPS Training Module that Mia gave entitled "3-Way Control Charts" in the "Quality Methods" course module series.

@mia_stephens "If the variability within subgroups is small compared to the subgroup-to-subgroup variability, the limits on the X-bar chart might not be appropriate."