Topics: Measure of Shape - Statistics


Given a variable , its skewness is a measure of how asymmetrical its data is with respect to its mean.

Let be observations of the variable . The skewness of is defined as:

…where is ’s standard deviation.

When skewness is negative, mass tends to be concentrated to the right of the mean (with a tail on the left); when it’s positive, it tends to be concentrated to its left (with a tail on the right):

(courtesy of Wikimedia Commons)

Negative and positive skew are sometimes referred to as left-skewed and right-skewed, respectively.