##### Definition

Standard deviation may be defined as the square root of the arithmetic average of the squares of deviations taken from the arithmetic average of a series.

##### Essential Features

From the above definition, the essential features of standard deviation may be outlined as under:

- The deviation of the items are taken from the arithmetic average of a series.
- Plus and minus signs are taken account while finding the deviation of the items.
- All the deviations are squared up to neutralize the reducing the deviation effect of the minus deviations.
- The square root of the average of the squared deviations are found out in order to neutralize the effects of squaring up of the deviations.