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kartikhpatel
Community Trekker

Cpk Analysis

Example   Dtata
98.8
99.7
99.7
99.9
99.5
100.0
100.4
98.8
99.3
100.5
100.4
100.5
100.2
100.4
101.5
100.7
100.7
100.4
99.7
100.3
100.4
101.2
101.2
100.0
99.7
100.3
101.4
101.0
100.5

Kindly Help For Above Data.

I want to find Within sigma estimated by moving range & Cpk. Please Help me.

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1 ACCEPTED SOLUTION

Accepted Solutions
louv
Staff (Retired)

Re: Cpk Analysis

If I assume that you are dealing with a one sided specification of >98% Assay for instance I can use either Quality and Process Control Chart Builder or an IR/MR control chart under the Analyze>Quality and Process platform.

12831_Screen Shot 2016-09-26 at 9.34.54 AM.png

12830_Screen Shot 2016-09-26 at 9.34.04 AM.png

7 REPLIES 7
Highlighted

Re: Cpk Analysis

I may have missed it, but do you have spec limits?

kartikhpatel
Community Trekker

Re: Cpk Analysis

Sprc Limit is 98 to 102.

For Within sigma JMP is using which Constant?

d2=? 1.1.28 or any other?

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louv
Staff (Retired)

Re: Cpk Analysis

If I assume that you are dealing with a one sided specification of >98% Assay for instance I can use either Quality and Process Control Chart Builder or an IR/MR control chart under the Analyze>Quality and Process platform.

12831_Screen Shot 2016-09-26 at 9.34.54 AM.png

12830_Screen Shot 2016-09-26 at 9.34.04 AM.png

kartikhpatel
Community Trekker

Re: Cpk Analysis

Thank you Mr Lou Valente For Reply.

But My Question is For Within sigma JMP is using which Constant?

d2=? 1.1.28 or any other?

@Lou Valente

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Steven_Moore
Super User

Re: Cpk Analysis

If I may add a point here:  If I assume your data is in time order (a requirement for a control chart), then you definitively have two populations in your data.  The first 9 data points comprise one population and the remaining 20 points comprise the second.  You can calculate Capability Indices for both populations separately, but to calculate a Capability for the entire data set is meaningless.  Any process must be in a "reasonable degree of statistical control" before one can calculate meaningful Capability Indices.  Your first question from this data set should be, "What happened to the process between somewhere around data points 9 and 10 that caused the process to shift upwards."  If the special cause of the shift is a good thing, you need to understand what the cause is and modify the system to make this permanent.

I hope this helps.

Steve
louv
Staff (Retired)

Re: Cpk Analysis

12847_Screen Shot 2016-09-27 at 10.13.20 AM.png

Steven_Moore
Super User

Re: Cpk Analysis

For individuals/moving range charts, you should always use the following formulas for computing limits:

Limits for Individuals chart = average ± 2.66 * average moving range

Upper limit for mR chart = 3.268 * average moving range

As Dr. Wheeler says in his articles on the right and wrong ways to do control charts, "Accept no other limits".

Steve
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