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# Distinct Categories in MSA

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  • #29061

    Stumped…
    Member

    Hi,
    Minitab and AIAG has what is referred to as the number of distinct categories in their discussions and analysis of MSA.
    They define it as: [(part st dev)/(measurement system std dev)] * 1.41
    Does anybody know the specific rationale for this, or is this one of those AIAG conventions that have been adopted? 
    Thanks!

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    #73504

    vin
    Member

    I believe that it basically defines how many different “buckets” you could reliably segregate product into i.e. Distinct Categories = 2, then it is a go-no-go gage;  Distinct Catergories = 3 means low, med, high, etc.
    By the way,  you need to round down to the nearest whole number after using the equation you listed.  As for the 1.41, I’m not sure, but I think that is probably derived from “the square root of the sum of the squares”, since 1.41 is the square root of 2.

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    #73506

    Stumped… no longer
    Member

    I found the answer… you can find it on Minitab’s web site:
    http://www.minitab.com/support/answers
    It is answer number 720.

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