The Lesson

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:

bar chart 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.

read off test scores from a bar chart
  • 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.

create a bar chart (from a frequency table)

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).

Bar charts can show different types of data. This bar chart shows discrete data.

Vertical and Horizontal Bar Charts

Bar charts can be vertical:

Bar charts can be vertical. Bar charts can also be horizontal:

Bar charts can be horizontal. Both bar charts present the same information. Which one you use is up to your personal taste.