Mention important measures of dispersion.

Measures of Dispersion:
(i) Range: Range is defined as the difference between two extreme observations i.e. the largest and the smallest value.
(ii) Inter quartile range: Inter quartile range is the difference between upper quartile and lower quartile.
(iii) Quartile deviation or Semi-Inter-quartile range: Quartile deviation is known as half of difference of third quartile  and first quartile . It is also known as semi inter quartile range.
(iv) Mean deviation: Mean deviation/average deviation is the arithmetic mean of the deviations of various items from their average (mean, median or mode) generally from the median.
(v) Standard Deviation: Standard deviation is the best and widely used measure of dispersion. Standard deviation is the square root of the arithmetic mean of the squares of deviation of its items from their arithmetic mean. 
(vi) Lorenz curve : The Lorenz curve devised by Dr. Max O. Lorenz is a graphic method of studying dispersion.