Measures of Dispersion
The dispersion may be defined as “the extent to which the magnitudes or qualities of the items differ,” that is, the degree of diversity. A distribution is not adequately described by knowing the measure of central tendency alone. Absolute dispersions are expressed in the units the measurements are made, whereas relative dispersion is a pure number expressed as a ratio or percentage. Dispersion is also expressed by fluctuation, spread, scatter, or variation. The distributions A (blue curve) and B (red curve) shown in Fig. 7.1 are distinct though these are having the same central value. This distinction is due to the change in their degree of dispersion. Dispersion or scatter is more in the case of A (blue curve) than in the case of B (red curve). Therefore, it becomes necessary to find out a suitable measure of central tendency to describe the structure of the data adequately and appropriately. The range, quartile deviation, mean deviation, and standard deviation are various measures of dispersion. Various methods of computations of measures of dispersion have been dealt with in this chapter.