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Help with Confidence Intervals

  1. #1
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    Help with Confidence Intervals

    Hi all,
    I would really appreciate your help with this discrepancy that I am not able to explain.

    If I go about finding the 95% confidence interval of a set of data by first finding the standard deviation/mean, I am getting a different answer than if I use the Data Analysis Tool --> Descriptive Statistics --> Confidence Level.

    For example, for the following data set (n = 16):

    14, 9, 11, 9, 14, 10, 13, 14, 15, 13, 11, 11, 10, 14, 11, 13.

    stdev = 1.966
    average = 12
    count = 16

    =confidence.norm(0.05,1.966,16) = 0.9635

    HOWEVER,

    When this set of data is plugged into the "Descriptive Statistics" Tool, I receive a "Confidence Level (95.0%) = 1.0478"

    Are these two things measuring separate variables that I am not noticing? How should I be interpreting this?

    Thank you in advance!

  2. #2
    Forum Guru MarvinP's Avatar
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    Re: Help with Confidence Intervals

    Hi excelhelp and welcome to the forum,

    Way back in my statistics years there was a "n" vs "n-1" that I never completely understood. If I recall the "n-1" was used to insure a better(?) answer. Is there a way you can do that in your normal formula to see if it comes out to the 1.0478 number?
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  3. #3
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    Re: Help with Confidence Intervals

    Hi, thank you for replying! Unfortunately I believe that 0.9635 was in fact the correct answer (which I confirmed externally with other websites like socscistatistics), so if anything the automated 1.0478 response is wrong.

  4. #4
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    Re: Help with Confidence Intervals

    Hi, thank you for replying! Unfortunately this did not work, as I explain in my response below.

  5. #5
    Forum Guru MarvinP's Avatar
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    Re: Help with Confidence Intervals

    Hi,

    Is this the function you are using? https://corporatefinanceinstitute.co...xcel-function/

    Read the bottom of the above link and are you using the Confidence.Norm function and which version of excel do you have? I believe the add-in changed a few times since older excel.
    Last edited by MarvinP; 03-10-2021 at 10:31 PM.

  6. #6
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    Re: Help with Confidence Intervals

    Hi you are correct. I am using Excel 16.45, and am indeed using the confidence.norm function.

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