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MSA question

Six Sigma – iSixSigma Forums Old Forums General MSA question

  • This topic has 4 replies, 3 voices, and was last updated 14 years ago by BC.
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  • #50037

    Snow
    Participant

    I executed a MSA and now have to analyse the results. From the ANOVA I found a GageR&R of 7.6%. And minitab also calculated the StudyVar to be 21.3%
    Isn’t this conflicting? How should I intepret the results?
    Thanks

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    #171861

    Craig
    Participant

    R&R / Study variation and R&R / tolerance are 2 different things.
    Is the 7.6% value your P/T ratio? (R&R / Tolerance)
     
    Need a little more detail in your question

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    #171862

    BC
    Participant

    Dude,
    There are two different Gage R&Rs:  %Contribution is a percent of total variance, and %StudyVar is a percent of total standard deviation.
    In the auto industry, we use the %StudyVar.
    As hacl mentioned, you can complicate this even more if you calculate GRR as a percent of tolerance.
    BC

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    #171933

    Snow
    Participant

    BC & Hacl thanks for you r reply,
    The MSA revealed 7.6% contribution on the variance and 21.3% Studvar – I understand the Math behind it. But what does this practically means, in plane English…?
    I appreciate your help
    thanks in advance
    D.

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    #171942

    BC
    Participant

    Dude,
    I hope this analogy explains it without telling you something you don’t already know. 
    It’s like a right triangle obeying Pythagoras’s theorem:  the sum of the squares of the legs equals the square of the hypotenuse.  Standard deviations are the lengths of the legs and variances are the squares of the lengths of the legs.
    So, assume the legs represent measurement and part variation.  The hypotenuse is total variation.  For ease of analogy, let’s say the measurement leg (GRR) is 3, the part-to-part leg is 4, and the hypotenuse is 5 (a 3-4-5 right triangle).
    Using StudyVar: GRR is 3/5 or 60%.  Part-to-part is 4/5 or 80%.
    Using Contribution: GRR is 9/25 or 36%.  Part-to-part is 16/25 or 64%
    Note that Contribution is the square of the SudyVar (0.6^2 = 0.36).  I don’t know why yours didn’t come out that way; I’d need to see the whole data set.  Maybe you’re mixing StudyVar and %Tolerance.
    So that’s all it is.  With contribution, the percentages will add to 100.  With StudyVar, they won’t.  But StudyVar is in the natural units of measure, and Contribution uses the square of them.  It’s your choice; whichever you prefer.  Auto industry uses StudyVar, because standard deviations are in the natural units.

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