For the study of dispersion, we need some measures which show whether the dispersion is small or large. There are two types of measure of dispersion which are:
(a) Absolute Measure of Dispersion
(b) Relative Measure of Dispersion
Absolute Measures of Dispersion:
These measures give us an idea about the amount of dispersion in a set of observations. They give the answers in the same units as the units of the original observations. When the observations are in kilograms, the absolute measure is also in kilograms. If we have two sets of observations, we cannot always use the absolute measures to compare their dispersion. We shall explain later as to when the absolute measures can be used for comparison of dispersion in two or more than two sets of data. The absolute measures which are commonly used are:

The Range

The Quartile Deviation

The Mean Deviation

The Standard deviation and Variance
Relative Measure of Dispersion:
These measures are calculated for the comparison of dispersion in two or more than two sets of observations. These measures are free of the units in which the original data is measured. If the original data is in dollar or kilometers, we do not use these units with relative measure of dispersion. These measures are a sort of ratio and are called coefficients. Each absolute measure of dispersion can be converted into its relative measure. Thus the relative measures of dispersion are:

Coefficient of Range or Coefficient of Dispersion.

Coefficient of Quartile Deviation or Quartile Coefficient of Dispersion.

Coefficient of Mean Deviation or Mean Deviation of Dispersion.

Coefficient of Standard Deviation or Standard Coefficient of Dispersion.

Coefficient of Variation (a special case of Standard Coefficient of Dispersion)
