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Pp,Ppk Cp,Cpk

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  • #46231

    Allthingsidiot
    Participant

    Please  define  the  real  difference  between Pp,Ppk & Cp,Cpk.
    Thanks

    0
    #152493

    Vidyadhar
    Member

    Check the following url
    https://www.isixsigma.com/ library/ content/ c010806a.asp

    0
    #152494

    Allthingsidiot
    Participant

    Please  explain  in  few words,don’t  compicate  things?thanks

    0
    #152496

    mcintosh
    Participant

    Cp and Cpk are used to define the snapshot capability index where Pp and Ppk are used to define the long term capability index. 
     
    If you are using minitab to calculate the capability, the difference in calculations are as follows;
    Cp and Cpk uses the within standard deviation which is estimated from the moving range average.
    Pp and Ppk use the overall standard deviation which is calculated using the actual standard deviation calculation.
    The way Minitab calculates Cp and Cpk it will somewhat ignor process shifts and trends.  Pp and Ppk will not.  In other words if the Cp and Cpk are much higher than the Pp and Ppk this is an indication that the process contains process trends or shifts (instabilities).
    I hope this helps,
    Tom

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    #152519

    Allthingsidiot
    Participant

    Thank You  Tom  for  your  informative  reply,regards

    0
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