The coefficient of variation (CV) is the ratio of the standard deviation to the mean and shows the extent of variability in relation to the mean of the population. The higher the CV, the greater the dispersion.
CV = Standard Deviation / Mean
The coefficient of variation is useful as it is dimensionless (i.e. independent of the unit in which the measurement was taken) and thus, comparable between data sets with different units or widely different means.
See also 'Accuracy Indicators'