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
