The third moment about the mean describes the *symmetry*, or the *skewness*, of the values in the distribution:

The *coefficient of skewness* is the usual dimensionless measure of symmetry:

The skewness (m_{3} and *C*_{s}) will be positive if positive differences (*X* – m) prevail over negative differences; this means that the right tail of p.d.f. is longer then the left tail, i.e. the distribution is skewed to the right. Negative skewness implies that the distribution is skewed to the left.