# Measures of Dispersion: Introduction

Another commonly encountered term in statistics is “Measures of Dispersion”.

What do we mean by “Measures of Dispersion”?

Dispersion refers to the spread of the data.

Let us look at an example to understand dispersion or spread.

Assuming the test scores of 10 randomly selected students from 3 classes were as follows:

Class 1: 20  20  20  20  20  20  20  20  20  20

Class 2: 20  21  22  23  20  20  19  18  17  20

Class 3: 20  20  20  20  20  20  21  20  19  20

If one were to take the average score of any class, we would get 20.

However, would you say that there was no difference between the performance of students of class 1 and that of students from class 2 or 3?

I’m guessing you would say that there is a difference.

Class 1 students all scored 20. Class 2 students’ scores went from 17 to 23. Class 3 students scored between 19 and 21.

So, although the average (mean) [ middle value] is a good value to have, it has some limitations.

Measures of dispersion tell us how the values vary around a central value. This in turn, gives an idea of the spread of the data.

Common measures of dispersion include Range, Standard deviation, Variance

Summary:

Measures of dispersion tell us how values are arranged or spread around a central value (like the mean).

Common measures of dispersion are Standard deviation, Range, Variance