33 Measures of Dispersion- II

S. Gandhimathi

1. STANDARD DEVIATION

Definition: Standard Deviation is the root mean square deviation of the values from their arithmetic mean.

The abbreviation of standard deviation is S.D. and s (read sigma) is the symbol. The concept of standard deviation was introduced by Karl Pearson in 1893. It removes mathematical deficiency of mean deviation to ignore negative sign. Most of the mathematical properties of dispersion is satisfied by the standard deviation. Hence it is a good measure of dispersion. It is the most widely used absolute measure of dispersion. The corresponding relative measure is Coefficient of Variation.

2.Methods of calculating standard deviation

1. Actual Mean Method
2. Direct Mean Method
3. Assumed Mean Method
4. Step Deviation Method

Formulae