What is a bar chart?
A wide application of bar charts from newspapers to books made them an easily understood tool for representing various information.
Bar chart (or bar graph, bar diagram) is a graphical representation of data which uses vertical or horizontal bar of different heights. It is a great tool for comparison of data among categories.
Every bar chart has two axes; x – axis (the horizontal axis) and y – axis (vertical axis). Data categories are shown on the horizontal axis, while the vertical axis represents the scale. The rectangular bars are the data series.
Bar charts can be vertical, horizontal or double.
When to use it
Bar charts are used for plotting discrete data; precisely, data which is not continuous and has discrete values. They are an excellent way of comparing items between different groups. The main goal is to represent the relation between the x – axis and y – axis.
There are many advantages of using bar charts, and one of them is surely possibility of representing data that shows changes over time. For example, a person might ask some group of people what is their favorite BMW car and then draw a pie chart which represents the percentages of people who prefer a certain type of car.
But, if we want to see how BMW’s preferences changed over time, we will use a bar chart. In other words, by looking at a bar chart, we could see which type of car customers prefer now and which they preferred ten years ago.
The vertical bar chart is the most common type of bar chart. We use them in situations when we want to display ordinal variables; for example, salary ranges.
We use horizontal bar charts when we want to display nominal variables; for example, favorite type of chocolate.
Double bar charts (or double bar graphs, multiple bar graphs) are used to compare more than one group. They also have two axes and we simply put the bars side by side.
Example 1: A survey which included $150$ students asked them: ”What is your favorite sport?”. The results are:
Construct a vertical and horizontal bar chart for the given table. Which sport is the most popular?
Sports represent data categories while number of students represents a scale.
Therefore, a vertical bar chart is:
A horizontal bar chart is:
Obviously, the most popular sport is football.
For easier reading, we can put numbers at the end of the bars:
Example 2: The following table shows student marks in two tests.
Construct a double bar chart for the given table.
Test $1$ represents first group that we observe, while Test $2$ represents the second group.
A double bar chart is:
By observing this bar chart, we can conclude that most of the students did better in test $2$ than in test $1$. Moreover, it is easier to conclude that by observing a double bar chart than the given table.