There are two kinds of measures of dispersion, namely
1. Absolute measure of dispersion
2. Relative measure of dispersion
Absolute measure of dispersion indicates the amount of variation in a set of values in terms of units of observations. Relative measures of dispersion are free from the units of measurements of the observations. They are pure numbers. They are used to compare the variation in two or more sets, which are having different units of measurements of observations. Standard Deviation is one of the methods of Absolute measure of dispersion.
Karl Pearson introduced the concept of standard deviation in 1893. Standard deviation is also called Root- Mean Square Deviation. The reason is that it is the square – root of the mean of the squared deviation from the arithmetic mean. It provides accurate result. Square of standard deviation is called Variance.
