Since standard deviation, mean, median, and mode are all absolute data on statistical samples, they do not permit a direct comparison of variation between samples with different means or different units of measurement.
One way to obtain a measure of variation that has no units is to divide the standard deviation (s) by the mean
(
), and multiply by 100 to give a percent. This quantity is called the coefficient of variation (CV), and can be used to compare methods that give different units.
For example, the coefficient of variation for two different glucose methods would be calculated as shown below after the mean and standard deviation for each method has been established. The hexokinase method has
= 99 mg/dL, and s = 8.0 mg/dL. The orthotoluidine method has
= 105 mg/dL, and s = 12.5 mg/dL.
From these CV's we would conclude that the hexokinase method is relatively more precise because it has a lower CV.
