iSixSigma

Ppk = Cpk

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  • #44963

    boettler
    Member

    can someone help me out with something?
    I have a customer who is telling me that a .83 Ppk is equivalent to a 1.33 Cpk.
    I have never heard of or experienced any direct coorelation between the two capability indexes.
    Am I missing something?
    thanks

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    #145287

    lin
    Participant

    You are not missing anything.  There is no direct correlation between the two.  Cpk is calculated using the estimated standard deviation from a range chart.  Ppk is calculated using the standard deviation calculated from all the data.  There is no correlation between those two standard devaitions, although they should be close to one another if the process is in control.  The more out of control the process is, the more difference there will be.
     
    Bill

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