Question

What is the formula to calculate the standard deviation of a sample?

Answer 1

`sigma = sqrt(1/Nsum (x_i - mu)^2)`

Explanation:

`mu` is the average of all `x_i`. The first deviation, sum of `x_i - mu` is by definition zero. The second deviation is the first to give us some information on the spread of values around the mean. Note it's a symmetric measure, it does not distinguish between values above or below the mean. Third deviation does. It's called the skewness.