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RMSEBird223
Level II

How to find out which formula was used if there are different formulas available based on different conditions?

Hi all,

 

I'm wondering if there's a way to find out which exact formula JMP used to calculated a certain value if there are several formulas available depending on different conditions.
For example, calculation of Cpk and Ppk values: Depending on whether the data is normally distributed or not, different formulas are used for their calculation (see links of JMP documentation below). And again for non-normal distributions, it depends on a certain condition which of the two formulas is finally used for Cpk and Ppk calculation. So is there a way to quickly trace back what JMP did to calculate Cpk and Ppk - without calculating it on my own?

 

Thanks for your help!

Cpk / Ppk for normal distributions: https://www.jmp.com/support/help/en/17.2/index.shtml#page/jmp/statistical-details-for-capability-ind...
Cpk / Ppk for non-normal distributions: https://www.jmp.com/support/help/en/17.2/index.shtml#page/jmp/statistical-details-for-capability-ind...


Note: I using JMP 18

1 ACCEPTED SOLUTION

Accepted Solutions
jthi
Super User

Re: How to find out which formula was used if there are different formulas available based on different conditions?

I would guess if you told JMP to use non-normal distribution it will tell what method was used. Otherwise it will assume normal distribution.

 

Using normal distribution (or no changes to distribution)

jthi_0-1726218777605.png

Told JMP to use nonnormal distribution

jthi_1-1726218889365.png

Normal is still visible on the left

jthi_2-1726218901015.png

From Process Screening -> Launch Process Capability -> Compare Distributions -> Selected as Mixture of 2 Normals (visible on top)

jthi_3-1726219029083.png

 

-Jarmo

View solution in original post

5 REPLIES 5
jthi
Super User

Re: How to find out which formula was used if there are different formulas available based on different conditions?

Where do you have your Cpk/Ppk values? For example in Process Capability (from distribution platform) it seems to be visible here

jthi_0-1726155370913.png

 

-Jarmo
RMSEBird223
Level II

Re: How to find out which formula was used if there are different formulas available based on different conditions?

Thanks for your reply. I use Cpk/Ppk calculation via the distribution platform (like you showed above) and via the process screening platform. What you showed in your example above is exactly what I was looking for. Unfortunately, I don't have this information if I run it on my side. I guess I have to change my preferences for the distribution platform

RMSEBird223_0-1726211238206.png

 

jthi
Super User

Re: How to find out which formula was used if there are different formulas available based on different conditions?

Have you told JMP to use something else than normal distribution?

-Jarmo
RMSEBird223
Level II

Re: How to find out which formula was used if there are different formulas available based on different conditions?

I just resetted the preferences of the distribution platform to default (I expect that JMP uses then the normal distribution) and, sadly, I still don't get the information which methods JMP uses to calculate the capability indices. But thanks for the suggestion!

jthi
Super User

Re: How to find out which formula was used if there are different formulas available based on different conditions?

I would guess if you told JMP to use non-normal distribution it will tell what method was used. Otherwise it will assume normal distribution.

 

Using normal distribution (or no changes to distribution)

jthi_0-1726218777605.png

Told JMP to use nonnormal distribution

jthi_1-1726218889365.png

Normal is still visible on the left

jthi_2-1726218901015.png

From Process Screening -> Launch Process Capability -> Compare Distributions -> Selected as Mixture of 2 Normals (visible on top)

jthi_3-1726219029083.png

 

-Jarmo