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Contribution vs Study Variation

Six Sigma – iSixSigma Forums Old Forums General Contribution vs Study Variation

This topic contains 2 replies, has 2 voices, and was last updated by  AT 13 years, 9 months ago.

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  • #40961

    AT
    Participant

    In interpreting a Gage R&R, which is the more appropriate parameter – contribution% or study variation% ? An example will help.

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    #128057

    CT
    Participant

    GR&R’s have different acceptance criteria, which is in part based on what you are trying to learn from them.
    For % Contribution you typical want an R&R with less than 9%
    For % P/TV you would want an R&R of less than 30%
    For % P/T you would want an R&R of less than 30%
    Percent Contribution is typically preferred because you can easily determine whether the gage or the appraiser make up the bulk of the variation.
    Total Process Variation is used to determine if you can measure your process variation well enough to validate its process improvments. Otherwise, tell one part from another. For example if you improve a process using a particular gage, from 1 CpK to 1.7CpK can your current gage accurately distinguish between the parts now? T/PV will validate that, 1.7CpK is a good number, where as if the gage does not have enough resolution to distinguish between the different parts then the 1.7 Cpk may be a bad number. 
    CT

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    #128084

    AT
    Participant

    OK. Thanks. But what does “Study Variation” really mean? Why is it different from the Contribution value? It comes by default in Minitab.

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