3  Basic Statistics

3.1 Sample Mean

\[\bar x = \frac{1}{n}\sum x_i = \frac{\sum x_i}{n}\]

3.2 Sample Standard Deviation

\[s_x = \sqrt{\frac{1}{n-1}\sum (x_i - \bar x)^2} = \sqrt{\frac{\sum(x_i -\bar x)^2}{n - 1}}\]

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]