Constructing Circle Graphs


Objectives

After completing this unit, you should be able to:

Introduction

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.

Sneakers Sold for November 1997
at The Shoe Source

Brand Name Number Sold

Adidas

150

Nike

192

Reebok

60

Asics

108

Other

90

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:

Constructing Circle Graphs

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.

Example

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

Sneakers Sold for November 1997
at The Shoe Source

Brand Name Number Sold

Adidas

150

Nike

192

Reebok

60

Asics

108

Other

90

Answer to Example

  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.

    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.

  1. 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.

    150 + 192 + 60 + 108 + 90 = 600 total shoes sold

  1. 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.

  2. 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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