Coefficient of variation

A measure of relative variability, equal to the standard deviation divided by the mean (Minitab multiplies the quotient by 100). Because it is a dimensionless number, It is useful in comparing the dispersion of populations with significantly different means.

For example, you are the quality control inspector at a milk bottling plant that bottles small and large containers of milk. You take a sample of each product and observe that the mean volume of the small containers is 1 cup with a standard deviation of 0.08 cup, and the mean volume of the large containers is 1 gallon (16 cups) with a standard deviation of 0.4 cups. Although the standard deviation of the gallon container is five times greater that the standard deviation of the small container, their coefficients of variation (COVs) support a different conclusion:

The coefficient of variation of the small container is over three times greater than that of the large container. In other words, although the large container has a greater standard deviation, the small container has much more variability relative to its mean.