## Quartile Deviation for ungrouped data

Quartile deviation is half the difference between the thrid quartile $Q_3$ and the first quartile $Q_1$ of a frequency distribution. It is also known as Semi-interquartile range.

## Formula

The quartile deviation is given by

### $QD=\dfrac{Q_3-Q_1}{2}$

and the coefficient of quartile deviation is given by

### Coeff. of $QD=\dfrac{Q_3-Q_1}{Q_3+Q_1}$

where

• $Q_1$ is the first quartile of the data
• $Q_3$ is the third quartile of the data