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Probability of points outside of the contorl limit

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  • #46108

    Whitehurst
    Participant

    How can I estimate the probability of a next point in a control chart will fall outside of the control limits?

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    #151948

    Adrian Smith
    Participant

    Assuming your control limits are at +/- 3 sigma the probability of a point falling outside the control limits is 0.27% (since +/- 3 sigma covers 99.73% of your data set).
    Rgds,Adrian
    http://adrian.smith.name
     

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    #151949

    Darth
    Participant

    Control limits are not probability limits.  Since data points are supposed to be independent, you can’t predict when the next data point will fall outside a control limit.  Once it does, you know the probability that it could have happenend by chance.

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    #151952

    Whitehurst
    Participant

    Thanks for your response .I agree

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