Capability Indices — Cpk

Section 4 Process Capability

Lesson S04-05

Text: Section 4 pages 22 – 31

Duration: 38 minutes

Introduction to Cpk

In order to assess two distinct features of the process, we need two estimates–one for location and one for variation. Unfortunately, this simple notion has been ignored, and many have the false impression that a Cpk can describe both aspects of the process distribution. Rather, the Cpk is just a Cp for the worst side of the distribution of individuals. We review the details next.

Is this a 4 sigma, 5 sigma, or 6 sigma process?

Calculation of Cpk

Now, calculate the Cp of this process.

Cp & Cpk Discussion

Which process has the higher PPM level?

Cp & Cpk Assumptions

What is the Cpk of this process?

Cp & Cpk & PPM

A Minitab Example

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About Steven Wachs

Steven Wachs has 25 years of wide-ranging industry experience in both technical and management positions. Steve has worked as a statistician at Ford Motor Company where he has extensive experience in the development of statistical models, reliability analysis, designed experimentation, and statistical process control.