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.
The quartile deviation is given by
and the coefficient of quartile deviation is given by
- $Q_1$ is the first quartile of the data
- $Q_3$ is the third quartile of the data