Coefficient of Skewness

Skew is a measure of asymmetry in the distribution. A positive skew indicates a longer tail to the right, while a negative skew indicates a longer tail to the left. A perfectly symmetric distribution, like the normal distribution, has a skew equal to 0. For small data sets this measure is unreliable.

Population Skew ()

$image\popskew.png$

Sample Skew ()

$image\samskew.png$

(adapted from King and Julstrom, 1982 and Hildebrand, 1986)

where

	= Population Standard Deviation
s	= Sample Standard Deviation
	= Population Mean
	= Sample Mean
N	= number of data values for a population
n	= number of data values for a sample
xi	= ith data value