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Error in standard deviation calculation

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  • Oktober 19, 2005 um 12:26 am Uhr #12658
    norbert.bakkers@lr.orgnorbert.bakkers@lr.org
    Teilnehmer

    When converting a standard deviation calculation (from the statistics menu) into a formula I noticed the following:
    The first part of the formula consists of ‘SQRT(n/(n-1))’, should this not be ‘SQRT(1/(n-1))’?

    Oktober 19, 2005 um 12:26 am Uhr #8321
    norbert.bakkers@lr.orgnorbert.bakkers@lr.org
    Teilnehmer

    When converting a standard deviation calculation (from the statistics menu) into a formula I noticed the following:
    The first part of the formula consists of ‘SQRT(n/(n-1))’, should this not be ‘SQRT(1/(n-1))’?

    Oktober 19, 2005 um 8:38 pm Uhr #9073
    Bernhard KantzBernhard Kantz
    Teilnehmer

    The formula is correct. The standard deviation can be written in to forms. One uses a factor 1/(n-1) and the other one a factor n/(n-1). If you convert the first formula into the second formula, you make use of the equation Sum(X) = n * Mean(X). This is where the factor n comes in.

    Oktober 20, 2005 um 9:57 pm Uhr #9074
    norbert.bakkers@lr.orgnorbert.bakkers@lr.org
    Teilnehmer

    Thank you for the explanation, it makes perfect sense now. I also made a formula using the standard deviation equation I know and they did indeed give identical results

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