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Homework Help: Calculating moments in MS Excel

  1. Sep 8, 2007 #1
    Hi,

    As part of a school project on statistics, I'm trying to calculate some parameters of collected data. I've the marks of 50 randomly sampled students in 6 subjects. I'm trying to calculate their skewness. Since the inbuilt Excel function to calculate skewness uses an estimator I've never seen, I'm using the standard estimator:

    [tex]\frac {\sqrt{n (n-1)}}{n (n-2)} \frac {\Sigma_i (x_i - \bar{x})^3}{s^3}[/tex]

    Though this is not unbiased, it's the best I have as I can not assume normality (which is creating a load of problems) because the population is heavily (-)vely skewed .

    In Excel, I've written the following formula:

    =(SQRT($A51*($A51-1))/(($A51-2)*$A51))*(SUM((D2:D51 - D53)^3)/POWER(D55,3))

    where D2:D51 contains the data, $A51 is n, D53 is the mean and D55 is the sd.

    Is this correct? It seems a pity Excel has no in-built functions to calculate moments. Also, one of the values is coming out to be -1.099, and I can't remember whether odd-order standardized moments can be less than -1 :redface:

    Thanks for your help. This is really important or me.

    Molu
     
  2. jcsd
  3. Sep 8, 2007 #2

    EnumaElish

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    From Excel help:


    If you have to use your formula, all you have to do is to multiply Excel's result with [tex]\frac {\sqrt{n (n-1)}}{n (n-2)}\times \frac{(n-1)(n-2)}{n}. [/tex]
     
    Last edited: Sep 8, 2007
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