|Class 11 Maths Statistics||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.
Quartile Deviation (Q.D) = (Q3 – Q1 )/2
48,49,50,50,50,51,52 runs : Here n=7, QD = (51-49)/2 = 1
0,25,26,50,50,99,100 runs : Here n=7, QD = (99-25)/2 = 37
The quartile deviation is a slightly better measure of absolute dispersion than the range. But it ignores the observation on the tails.