* The three measures of dispersion are
(i) Range
(ii) Mean Deviation
(iii) Standard Deviation
* Range (Ungrouped Data): The difference between the maximum and minimum values of the series of observations.
* Range (Grouped Data): The approximate difference between the upper limit of the largest class and the lower limit of the smallest class.

* Mean Deviation (Ungrouped Distribution):
(i) Mean Deviation about mean = 
(ii) Mean Deviation about median = 

* Mean Deviation (Grouped Data):
(i) Mean Deviation about mean = 
(ii) Mean Deviation about median = 

* Variance and Standard Deviation for ungrouped Data:
    

* Variance and Standard Deviation of a discrete frequency distribution:
           

* Coefficient of Variation =