Measures of Dispersion (Variation)

A measure of dispersion is to measure the spread among values of observations in a data set. There are three commonly used measures of dispersion: variance, range and standard deviation.

Range

Range is the easiest measure of dispersion. It is the difference amongst the largest and the smallest value of observations in a data set.

        Range = Largest value -Smallest value

Example 

Calculate the range of the following data:

Students Exam marks

A 80

B 67

C 44

D 57

E 92

F 79

Solution:

=  92 - 44 = 48

The range is very easy to compute, but because it depends only on the largest and the smallest values, it is not as useful as the other measures of the variation which use every value.