The extent to which the observations in a sample or in a population vary about their mean is known as dispersion. A quantity that measures dispersion in a sample or population is known as a measure of dispersion, scatter or variability. There are two types of measure of dispersion that are absolute and relative dispersion. An absolute measure of dispersion is one that measures the dispersion in terms of the same units or square of the units, as the units of data. For example, if the unit of the data are in rupees, meters , kilogram etc., the units of measure of dispersion will also be in rupees, meters, kilogram etc. A relative measure of dispersion is one that is expressed in the form of ratio, coefficient or percentage and is independent of the measure of units. The main measure of dispersion are the range, the semi inter quartile range or the quartile deviation, the mean deviation or the average deviation, the variance and standard deviation.