Which measure is known as the relative dispersion measure?

The correct answer is the Coefficient of Variation, which is recognized as a relative dispersion measure. This statistic expresses the standard deviation as a percentage of the mean, thereby providing a dimensionless number that allows for comparison of variability between datasets that may have different units or means. This makes it particularly useful for comparing the degree of variation from one data series to another, even if the means are drastically different.

In contrast, standard deviation and absolute average deviation are absolute measures of dispersion; they provide information about the spread of data in its original units. While these measurements are beneficial for understanding how data points are distributed around the mean, they do not offer a means to compare variations across different data sets directly.

The variability index is not as commonly defined or used in the same context as the other measures mentioned. Overall, the Coefficient of Variation's ability to highlight the relative size of variability relative to the mean distinguishes it as the appropriate relative dispersion measure.