# Formulas > Descriptive Statistics > Skewness

Skewness is a measure of assymetry of a distribution. A positive skew indicates that the right tail is longer and the mass of the distribution is concentrated on the left. A negative skew indicates that the left tail is longer and the mass of the distribution is concentrated on the right.

The formula for unbiased skewness is

where
= data set
= number of data values in
= mean of the data set
= standard deviation of the data set

The formula for biased skewness is