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Quartile Deviation:
It is based on the lower quartile  and the upper quartile . The difference  is called the inter quartile range. The difference  divided by  is called semi-inter-quartile range or the quartile deviation. Thus
Quartile Deviation (Q.D) 
The quartile deviation is a slightly better measure of absolute dispersion than the range. But it ignores the observation on the tails. If we take difference samples from a population and calculate their quartile deviations, their values are quite likely to be sufficiently different. This is called sampling fluctuation. It is not a popular measure of dispersion. The quartile deviation calculated from the sample data does not help us to draw any conclusion (inference) about the quartile deviation in the population.
Coefficient of Quartile Deviation:
A relative measure of dispersion based on the quartile deviation is called the coefficient of quartile deviation. It is defined as
Coefficient of Quartile Deviation 
It is pure number free of any units of measurement. It can be used for comparing the dispersion in two or more than two sets of data.
Example:
The wheat production (in Kg) of 20 acres is given as: 1120, 1240, 1320, 1040, 1080, 1200, 1440, 1360, 1680, 1730, 1785, 1342, 1960, 1880, 1755, 1720, 1600, 1470, 1750, and 1885. Find the quartile deviation and coefficient of quartile deviation.
Solution:
After arranging the observations in ascending order, we get
1040, 1080, 1120, 1200, 1240, 1320, 1342, 1360, 1440, 1470, 1600, 1680, 1720, 1730, 1750, 1755, 1785, 1880, 1885, 1960.
Quartile Deviation (Q.D) 
Coefficient of Quartile Deviation 
Example:
Calculate the quartile deviation and coefficient of quartile deviation from the data given below:
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Maximum Load
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Number of Cables
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Solution:
The necessary calculations are given below:
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Maximum Load
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Number of Cables
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Class
Boundaries
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Cumulative
Frequencies
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 lies in the class 
 
Where  ,  ,  ,  and 
 
 lies in the class 
 
Where  ,  ,  ,  and 
 
Quartile Deviation (Q.D) 
Coefficient of Quartile Deviation 
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