Quartile Deviation: The QD is half of the difference between the upper and lower quartiles. Symbolically,
QD= ½ (Q3- Q1)
Quartile Deviation is an absolute measure of dispersion. The relative measure corresponding to QD, called the coefficient of QD, is obtained by applying the following formula:
Coefficient of Range= (Q3 - Q1) / (Q3 Q1)
Coefficient of QD can be used to compare the degree of variation in different distributions.
Merits of Quartile Deviation:
1. It is based on 50% of the observations.
2. It is not affected by the presence of extreme values.
3. In case of open-end distribution, it can be computed.
Demerits of Quartile Deviation:
1. It is not based on each and every item of the distribution.
2. It is not capable of further algebraic treatments.
3. The value of Range is affected more by sampling fluctuations