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Confidence Interval

Six Sigma – iSixSigma Forums Old Forums General Confidence Interval

This topic contains 1 reply, has 2 voices, and was last updated by  Lee 14 years, 1 month ago.

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  • #40803

    lin
    Participant

    I monitor a test by running a standard each day and monitoring the results using an Xbar-R chart.  I now have 20 subgroups, a total of 60 individual samples.  I want to see how close the average is to the reference value for the standard.  If I use the one sample t test:
    X +/- t(sigma)/sqrt(n)
    what should I use for the degrees of freedom and sigma?  Based on the subgroup averages or the individual results?  Or does it matter?
    Thanks.

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    #127802

    Lee
    Participant

    Sigma is the standard deviation of your data and the degree to freedom is your sampe size minus 1.
    Hope that helps!
    Eugene

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