3  Basic Statistics

3.1 Sample Mean

$$\overline{x}=\frac{1}{n}\sum x_i=\frac{\sum x_i}{n}$$

3.2 Sample Standard Deviation

$$s_x=\sqrt{\frac{1}{n-1}\sum (x_i-\overline{x}{)}^2}=\sqrt{\frac{\sum (x_i-\overline{x}{)}^2}{n-1}}$$

Interpretation of Standard Deviation

The [variable in the context of the problem] typically varies by [value of SD] from the mean of [value of the mean]