cpK/ppk

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Joined:

Mar 31, 2017

Is it correct to calculate cpk when I have no subgroup in the process data (grouping=1), meaning the sampling is continous, like tablet weight taken one after the other in one lot? How is cpk calculated in this case (the withingroup variation)?

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Accepted Solutions

Joined:

Jun 5, 2014

Solution

Correct? That's a different question. The 'correctness' of an approach is dependent on many aspects to the process capability analysis problem. For example: 1. Does your process data exhibit any evidence of assignable cause variation? 2. Does your data appear to be normally distributed? The answer to these questions influences the approach that is optimal for calculating process capability indices over and above the sheer mathematics associated with the reference in my first reply.

3 REPLIES

Joined:

Jun 5, 2014

Here's a reference for you in the JMP Online Documentation.

http://www.jmp.com/support/help/13/Capability_Analysis_2.shtml#1161749

As of January 2018, use this link:

http://www.jmp.com/support/help/13-2/Capability_Analysis_2.shtml#1161749

Joined:

Jun 5, 2014

Solution

Correct? That's a different question. The 'correctness' of an approach is dependent on many aspects to the process capability analysis problem. For example: 1. Does your process data exhibit any evidence of assignable cause variation? 2. Does your data appear to be normally distributed? The answer to these questions influences the approach that is optimal for calculating process capability indices over and above the sheer mathematics associated with the reference in my first reply.

Community Trekker

Joined:

Mar 31, 2017

Thank You

Data are normal distributed with no assignable cause variation. I assume the answer I was looking for (found in Process Capability in JMP 2012) is that if I do not group data JMP will automatically use moving range subgroup size 2 to calculate cpk.

KR