iSixSigma

Variance

Viewing 16 posts - 1 through 16 (of 16 total)
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  • #53668

    Chauffe
    Participant

    In the event I have a standard deviation of 0 (zero), no variance, what should I ask myself and what will the Pp, Ppk values be?

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    #191028

    Mikel
    Member

    Get a better measurement system. There is no such thing as 0 variance.

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    #191029

    Nick
    Participant

    I agree. If you are seeing no variance whatsoever then either your process is flawless or your measurement system needs some attention as it is unable to detect the variation.

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    #191030

    Chauffe
    Participant

    So if my Upper Spec is 140 and Lower Spec is 100, and all data measurements are 115, SD is 0, are the Pp, Ppk values NA?

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    #191031

    Nick
    Participant

    I think what Stan and I meant are that the computing the Pp and Ppk would be senseless because the measurement system is not adequate and should not be trusted.

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    #191032

    Chauffe
    Participant

    Thanks Guy’s!!!

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    #191033

    Rhill
    Participant

    Stan, you tard.

    Why are you sendingMack of on a measurement boondoggle. Of COURSE there’s no such thing as zeroo variance, but there is such a thing as an MSA %study variance and a Gage r&R. His measurement system may be just fine.

    Mackie, use 6 for your Ppk and dare your customer to challenge you.

    Peace.

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    #191034

    Mikel
    Member

    Miker,

    It’s retard, not tard.

    That’s like calling you a fus instead of the dufus you really are.

    You can’t pass GR&R with 0 variance in your sample and if his current system says there is no variance that has to be what his sample is.

    The advice to claim 6 is just stupid. It’s always great to see advice coming from people who don’t know Jack.

    He needs to have discrimination in his measurement system, he has none.

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    #191035

    Schwarz
    Participant

    There is such a thing as zero variance.

    An hour ago I counted the money in my wallet. It was $21. Thirty minutes ago, I counted it again. Still $21. Just now, I counted it again. Still $21.

    Over that hour period, the variance of the amount of money in my wallet is zero.

    Of course, the variable of interest here is not stochastic and so it doesn’t fall under the general definition of things that are studied and discussed in this forum. My point is that ‘non-changing’ entities, measured without error, can have zero variance.

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    #191036

    Mikel
    Member

    Dave, you are right. What a deep and heady answer.

    It’s like if I measured the value of your answer 20 times. It had no value all 20 times. Zero variance!

    Now to the useful world and process improvement. There is no such thing as zero variance.

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    #191037

    Schwarz
    Participant

    Stan, Of course you understand that my reply was an intellectual exercise and not advise to the forum or the original poster. It points out that some processes can be devised that do not vary over the measurement period. Whether to call the variance zero or undefined can be debated.

    Obviously in quality measurement scenarios involving stochastic processes, the run-to-run variance is not zero. Sample data that is identical for each measured value is probably due to a badly designed test or defective measuring instrument.

    Once a year I survey the maturity level of this forum and community. I see it has not improved. See you next year.

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    #191039

    MBBinWI
    Participant

    DaveS002 wrote:

    There is such a thing as zero variance.

    An hour ago I counted the money in my wallet. It was $21. Thirty minutes ago, I counted it again. Still $21. Just now, I counted it again. Still $21.

    Over that hour period, the variance of the amount of money in my wallet is zero.

    Of course, the variable of interest here is not stochastic and so it doesn’t fall under the general definition of things that are studied and discussed in this forum. My point is that ‘non-changing’ entities, measured without error, can have zero variance.

    I’m with Stan on this one – your answer was just plain stupid.

    Everyone knows you need three operators to do a GR&R :laugh:

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    #191040

    MBBinWI
    Participant

    Methinks this was a homework question. You should do your own work.

    If you want to submit a reasoned out answer and ask if you’ve followed a logical/appropriate path, that’s one thing. But don’t just sling out your homework question and expect us to answer it for you.

    Jeesh. You’d think that people would get a clue.

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    #191041

    MBBinWI
    Participant

    On second thought, let me measure your money. I bet that it will be a different value!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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    #191084

    Savage
    Participant

    To answer the original question, Pp and Ppk would typically be defined as n/a since they can not be calculated when the standard deviation of the individual values = 0. (You can not use 0 as the denominator and get a number. Your calculator would show this as an error and Excel would list the answer as “#DIV/0!)

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    #191085

    MBBinWI
    Participant

    Matt wrote:

    To answer the original question, Pp and Ppk would typically be defined as n/a since they can not be calculated when the standard deviation of the individual values = 0. (You can not use 0 as the denominator and get a number. Your calculator would show this as an error and Excel would list the answer as “#DIV/0!)

    Actually, the answer, using your logic, would be infinity, since anything divided by zero is infinite.

    This was just a sloth trying to get others to do his thinking for him (or his homework, which amounts to the same thing).

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