# Help with Sample Skewness

1. Jul 25, 2010

### FrostScYthe

Hi everyone,

I'm using the following formula to calculate skewness

$$g_1 = \frac{m_3}{m_2^{3/2}} = \frac{\tfrac{1}{n} \sum_{i=1}^n (x_i-\overline{x})^3}{\left(\tfrac{1}{n} \sum_{i=1}^n (x_i-\overline{x})^2\right)^{3/2}}\ ,$$

However, when I try excel on to calculate skewness I get a different results. For example this set:

1
1
1
1
1
1
1
9
9

I get: 1.33630621
Excel gets: 1.619847741

Is excel using a different formula, or am I doing something wrong?

Ted.

2. Jul 28, 2010

I believe Excel uses this:

$$\frac n {(n-1)(n-2)} \sum{\left(\frac{x - \bar x}{s}\right)^2}$$

3. Jul 29, 2010

### FrostScYthe

Any particular reason why
excel uses a different formula?

Ted.

4. Jul 29, 2010