The ________ is used to compare the variability of two or more data sets with different scales.

A) coefficient of variation
B) variance
C) median
D) coefficient of skewness

The coefficient of variation is a standardized measure of variability, calculated as the ratio of the standard deviation to the mean. It is useful for comparing the variability of data sets with different scales, because it normalizes the differences in scale by expressing the variation relative to the mean. Variance and median are measures of central tendency and dispersion, respectively, but do not serve the function of comparing variability across different scales. The coefficient of skewness is a measure of the asymmetry of a probability distribution, and does not directly compare variability across different data sets.