Double Bar Graph

A double bar graph, or a side-by-side bar graph, is a visual representation showing two sets of interrelated data using bars of different colors or shades. Most often, the x-axis shows the categories being compared for the two groups, while the y-axis shows the scales used for comparing the values.

A double bar graph is made in the same way as a single bar graph. It can be vertical or horizontal. Also, there is a key that gives the color of the bar that represents each group.

How to Make a Double Bar Graph

While making a double bar graph, we should follow the following steps:

1. Determine the number of categories and groups
2. Determine which category has the highest and the lowest value
3. Determine other categories like half and equal values
4. Plotting the graph in Excel or any other plotter

Example

A survey was conducted on the marks obtained by Daniel and John in the 5 subjects studied at St. Johns High School. The result is given in the table below.

Let us represent the following data using the double bar graph.

	Marks Obtained
Subjects	Daniel	John
English	92	72
Mathematics	98	80
Physics	68	91
Chemistry	70	98
Biology	56	75

It is a comparative data, best represented using a vertical double-bar graph.

If we analyze and interpret the graph, we can answer questions related to it.

Questions

Let us suppose your teacher asked you the following question:

a) Find the highest mark obtained by Daniel in a subject.

b) Find the lowest mark obtained by John in a subject.

c) Name the subject in which there is a maximum difference in the marks obtained by them and by how much.

d) Name the subject with the least difference in the marks obtained by Daniel and John.

Answers

a) To answer the question (a), we will see the longest bar in pink.

Here, we see that the pink bar in Mathematics is the highest. Thus, it is the highest mark obtained by Daniel in a subject. The marks (in the y-axis) corresponding to the bar are found to be 98.

b) To answer question (b), we will see the shortest bar in red.

Here, we see that the red bar in English is the shortest. Thus, it is the lowest mark obtained by John in a subject. The marks (in the y-axis) corresponding to the bar are 72.

c) To answer the question (c), we will see the maximum difference between a pair of pink and red bars. 

Here, we see that the difference is highest in biology.

To find the difference, we will record the marks obtained by Daniel and John in biology and then find the difference between them.

Here,

Marks obtained by Daniel in Biology = 98

Marks obtained by John in Biology = 75

The difference is:

=> 75 – 56 = 19

d) To answer the question (c), we will see the least difference between pink and red bars. 

Here, we see that the difference is the least in Mathematics.

To find the difference, we will record the marks obtained by Daniel and John in Mathematics and then find the difference between them.

Here,

Marks obtained by Daniel in Mathematics = 56

Marks obtained by John in Mathematics = 80

The difference is:

=> 98 – 80 = 18

The same graph can also be represented in the horizontal form.

E.g.1. Plot the given data showing the production of some cash crops in the years 2022 and 2023 in California using the double bar graph.

	Production (in tonnes) in California
Cash Crops	Daniel	John
Rice	50000	72000
Wheat	36000	18000
Maize	68000	21000
Bajra	43000	31000
Barley	56000	34000

By plotting the above data in the form of a double bar graph, we get the following: