# Homework Help: Calculating moments in MS Excel

1. Sep 8, 2007

### loom91

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:

$$\frac {\sqrt{n (n-1)}}{n (n-2)} \frac {\Sigma_i (x_i - \bar{x})^3}{s^3}$$

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

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

Molu

2. Sep 8, 2007

### EnumaElish

From Excel help:

If you have to use your formula, all you have to do is to multiply Excel's result with $$\frac {\sqrt{n (n-1)}}{n (n-2)}\times \frac{(n-1)(n-2)}{n}.$$

Last edited: Sep 8, 2007