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Cpk from median charts

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  • #53586

    Jaime
    Participant

    Have a good day,
    Can I calculate Cp, Cpk, Pp and Ppk index from median-range charts data?. If no, why not?. Thanks.

    Buen día,
    ¿Puedo calcular los indicadores Cp, Cpk, Pp y Ppk a partir de los datos de una carta de medianas-rangos?. Si no, ¿Porqué no?. Gracias

    JCastillo

    0
    #190789

    Anawis
    Participant

    Yes, you can calculate capability for median range charts. You need to calculate the sigma differently than for average range charts. For sigma, calculate MRx/d4(w) where w is the number of observations in the moving range. You’ll need to get a table of d4 values from a text such as Advanced Topics in Statistical Process Control by Donald Wheeler or even easier, use a software package such as JMP or Minitab to do the whole capability calculation for you.

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    #190792

    Jaime
    Participant

    Thanks for your response,
    I am using median-range charts and subgroup size is three pieces. I am using SPC second edition formulas on page 85, but I am calculating capabilty index with average-range formulas. I am not using median-moving range charts. I have Minitab 13.
    Is it the correct way for doing it? Thanks.

    JCastillo

    0
    #190797

    Rohatgi
    Participant

    Yes ! You can calculate

    0
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