Like any other measure of dispersion, standard deviation can also be measured in two ways viz. : (1) absolute and (2) relative. Absolute standard deviations are computed in the line discussed above. But they are not suitable for making a comparative study of more than one series. For this purpose, relative standard deviations are to be computed. A relative standard deviation is again of two types. They are:
- Co –efficient of standard deviation, and
- Co-efficient of variation.
- Co –efficient of standard deviation. This is expressed as the ratio of the absolute standard deviation to the arithmetic average of the series. This is represented as under :
Coeff. S.D = Standard Deviation/Mean or
Co-efficient of variation.The cp-efficient of standard deviation thus expressed does not give the answer in a convincing manner. To get the answer in a more convincing manner, co-efficient of variation is found out , which is expressed as the percentage of standard deviation of the arithmetic average of the series. Thus it is represented as under:
The co-efficient of variation guides us in ascertaining the relative degree of variability, or stability of a series. A series with more co-efficient of variation is regarded as less table, or less consistent than a series with less co-efficient of variation.