Bar Charts
What Is a Bar Chart?
A bar chart (or bar graph) is a chart which uses bars to present data.
The height of each bar shows how often each value appears in the data.
Dictionary Definition
The Oxford English Dictionary defines a bar chart as "a statistical diagram in which numerical quantities are represented by the height or length of rectangles of equal width, drawn usually side by side along an axis."
A Real Example of a Bar Chart
The image below shows a bar chart. It represents the test scores of a class of students:
We can find out what test scores the students achieved by reading off from the bar chart.
Reading from a Bar Chart
Reading from a bar chart is easy. The height of the bar above each test score tells us how many students achieved that test score.

The blue bar is above a Score of 5. It has a height of 2 (as measured on the Frequency axis).
This means that 2 students have a test score of 5.

The orange bar is above a Score of 6. It has a height of 3.
This means that 3 students have a test score of 6.

The green bar is above a Score of 7. It has a height of 2.
This means that 2 students have a test score of 7.
Creating a Bar Chart
Creating a bar chart is easy. We need to know how many times each value in a set of data appears.
It is useful to create a frequency table of the data first and then create a bar chart from it.
Bar Charts and the Types of Data
Bar charts can present the different types of data.
Data can be qualitative (which is described in words) or quantative (which is described in numbers).
Quantitative data can be discrete (which can only take certain values) or continuous (which can take any value, within a range).