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CI for StDve in Excel

Six Sigma – iSixSigma Forums General Forums Tools & Templates CI for StDve in Excel

This topic contains 4 replies, has 2 voices, and was last updated by  Örtlund 9 years, 7 months ago.

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  • #53344

    Örtlund
    Participant

    Hello

    Does anyone know the commando for calculating CI for StDve in excel?

    0
    #189693

    gbreader
    Participant

    Did you check out MS excel’s helpfile? This is what MS states…

    The CONFIDENCE(alpha, sigma, n) function returns a value that you can use to construct a confidence interval for a population mean. The confidence interval is a range of values that are centered at a known sample mean. Observations in the sample are assumed to come from a normal distribution with known standard deviation, sigma, and the number of observations in the sample is n.

    SYNTAX

    CONFIDENCE(alpha,sigma,n)

    Parameters: Alpha is a probability and 0 < alpha < 1. Sigma is a positive number, and n is a positive integer that corresponds to the sample size.

    Typically, alpha is a small probability, such as 0.05.

    0
    #189696

    Örtlund
    Participant

    Yes, thats for the population mean,
    What I am looking for if there is a comand/function to calculate CI for the StDev (sigma)?

    0
    #189698

    gbreader
    Participant

    Found at http://www.graphpad.com/faq/viewfaq.cfm?faq=1381

    Computing the Ci of a SD with Excel

    These Excel equations compute the confidence interval of a SD. N is sample size; alpha is 0.05 for 95% confidence, 0.01 for 99% confidence, etc.:

    Lower limit: =SD*SQRT((N-1)/CHIINV((alpha/2), N-1))

    Upper limit: =SD*SQRT((N-1)/CHIINV(1-(alpha/2), N-1))

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    #189699

    Örtlund
    Participant

    Thanks a lot!
    So there are probably non direct commands then?
    O well, This will do the work also.
    :)

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