Page "Skewness" Paragraph 10

where μ < sub > 3 </ sub > is the third moment about the mean μ, σ is the standard deviation, and E is the expectation operator.

The last equality expresses skewness in terms of the ratio of the third cumulant κ < sub > 3 </ sub > and the 1. 5th power of the second cumulant κ < sub > 2 </ sub >.

This is analogous to the definition of kurtosis as the fourth cumulant normalized by the square of the second cumulant.