Constructing Circle Graphs

After completing this unit, you should be able to:

• Construct a circle graph from a table of information.
• Critically read circle graphs, particularly to compare parts to a whole.
  

Using a circle graph to display categories of information can provide a quick and easy way to display information about the relationship of parts to whole. In this unit we will discuss how to go about constructing a circle graph when we are given data in a table form. (NOTE: If information is given in paragraph form we would first construct a table, as described in the first unit of this review, and then construct the circle graph.)

When we are given a table of information we first need to determine if it is the kind of information that would be suitable for a circle graph. The types of data that are suitable are frequencies (amounts), and percentages. Let's look at data given in the table.

By looking at the table we can see that Nike and Adidas have the largest sectors of sneaker sales, but constructing a circle graph would help us to view this quickly. To create a circle graph we need to determine the following:

• What is the "whole."
  
• How many different parts, or groups, are there.
  
• What percentage does each part, or data group, have of the whole.
  

When constructing a circle graph, follow the steps below (NOTE: If the data is not already in a table, put it into tabular form.):

1. Is the Data Suitable--Determine if there is a "whole" for the data. Then determine what the different parts, or data groups, of the whole are.
2. Calculate Percentages--For data that is not already given as a percentage, convert the amounts for each part, or data group size, into a percentage of the whole. (NOTE: If you need review on how to convert parts of a whole into a percent, you should review Book II of this series.)
3. Draw the Graph--Draw a circle and draw in a sector for each data group. Try to make the sector sizes look as close to the percentage of the circle as the percentage of the data group. (NOTE: We will explain a way to make a circle graph, approximating the sectors of a circle. If you are constructing a circle graph for publication or presentation you will need to be this accurate.)
4. Title and Label the Graph--Label the sectors with the data group name and percentage. Then add a title to the graph. This is the same as the title of the table.
   

Construct the circle graph for the data in the table below.

1. Is the Data Suitable:

   Determine whether there is a "whole" for the data. Then determine what the different parts, or data groups, of the whole are.

   • Define the whole--In this table, the whole is the total number of sneakers sold for the month of November 1997.
     
   • How many different parts, or groups, are there--There are five parts to the whole. Each data group is a category of sneaker brands (1) Adidas, (2) Nike, (3) Reebok, (4) Asics, (5) Other.

   From the table we can calculate the whole, and we do have different parts. This means the data could be displayed in a circle graph.

2. Calculate Percentages

   For data that is not already given as percentages, convert the amounts for each part, or data group, into a percentage of the whole.

   • Calculate the whole--This total can be found by adding up the numbers sold for each type of sneaker.
     There are five different parts to our whole. The table lists the number sold in each part. To find the total sold we add up these parts. When we do this, we find the total number is 600.
   150 + 192 + 60 + 108 + 90 = 600 total shoes sold
   • Calculate the percentage for each part--This means we must calculate the percentage of the whole for each of the five data groups. Since we now have the total number of sneakers sold, and we have the amount of each category sold, we can calculate the percentage of sales for each data group.
     Once we find the total, we can convert each Number Sold into a percentage of the whole. Lets go through the calculation for Adidas shoes. If look at Adidas shoes, 150 of the 600 shoes sold are Adidas.
      
     

     Brand Name	Number Sold
     Adidas	150

     
      
     This means the fraction of shoes sold that are Adidas is 150/600. To convert this fraction to a decimal, we divide the numerator by the denominator and then multiply by 100.
     So Adidas accounts for 25% of the sneakers sold last in November 1997. The table below has the percentages added for each category of sneakers

     Brand Name	Number Sold	Percentage Sold
     Adidas	150	25
     Nike	192	32
     Reebok	60	10
     Asics	108	18
     Other	90	15

3. Draw the Graph
   

   First, draw a circle. Then, draw in the sectors of the circle. We need to try make each sector correspond to the percentage of whole that it represents. For this circle our sectors need to be 32%, 25%, 18%, 15%, and 10%. You can also add shading to the sectors. This helps to make them easier to distinguish.

4. Title and Label the Graph
   

   Label the sectors with the data group name and percentage. Then add a title to the graph. This is the same as the title of the table. At the right we have the completed circle graph. This allows us to evaluate the relative sizes of group quickly. We can see that Nike has the largest percentage of sales, and that, of the top four sellers, Reebok has the smallest, approximately 1/3 that of Nike.

   Sneakers Sold for November 1997 at The Shoe Source

You should now be ready to try constructing a circle graph. Try the practice before moving on to the next unit.

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