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Coefficient of Variation (CV)

The coefficient of variation or CV of a variable is its standard deviation divided by its average.  It is frequently multiplied by 100 and reported on a percentage basis.  For many products and processes, the standard deviation increases as the average is increased.  An example is fill volume for a filling process.  This type of process is better characterized by its CV.  For example a CV of 3% means, regardless of the average, the standard deviation is 3% of the average.
When the standard deviation increases with the average, plots and effects tables of the standard deviation and average will look similar.  In this case plots and effect tables of the average and CV will prove more useful in understanding the effects of the inputs.