"The standard deviation is the square root of the arithmetic mean of the squares of all deviation. Deviations are measured from arithmetic mean of the items”.
Demerits—:
(i) Difficult—The process of squaring the deviations and then to find the value of its square root is a time consuming affair. It is quite difficult too.
(ii) More important to extreme values—In calcu-lation of Standard deviation un-due importance is given to marginal values.