Part I Review of Circle Graphs

Reading Circle Graphs(pie charts)

Circle graphs, also called pie charts, are a type of graph used to represent a part to whole relationship.

• They are circular shaped graphs with the entire circle representing the whole.

• The circle is then split into parts, or sectors.

• Each sector represents a part of the whole.

• Each sector is proportional in size to the amount each sector represents, therefore it is easy to make generalizations and comparisons.

An example of a circle graph is given below.

Revenue Sources for the Federal Government

When reading this circle graph we look for the following pieces of information: the graph title, individual sectors and their relative sizes, and the sector labels (one for each sector). Let's take a closer look at each of these.

Graph Title--A graph title gives an overview of the information displayed in the graph. The title is given at the top of the graph. Sectors--Each sector represents one part of the whole. The size of each sector represents its fraction of the whole. Sector Labels--The label of each sector indicates the category of information it refers to, and may also give numeric data (often a percentage) so we know the size of each sector.

Let's use the circle graph given here as an example of how to get information from a circle graph. Looking at the elements of this graph we find:

• Graph Title--The title gives an overview of the information displayed in the graph. The title of this graph is:

Revenue Sources for the Federal Government

We would expect the graph associated with this title to contain the names of different sources of revenue for the federal government, with some information on the relative amounts from each revenue source.

• Sectors- Each sector represents one part of the whole.

  The graph below contains four different sectors. This means the graph displays four different sources of revenue. The largest sector is a little less than half of the whole circle. There is another source that is also relatively large, and then there are two smaller sources of revenue.

• Sector Labels--Sector labels indicate the category of information represented in the sector and may also give numeric data (often a percentage).

The graph has a label for each sector. Each label shows what type of revenue it corresponds to, and the percentage of the whole for that sector. From the graph we can see:

The largest sector, 45% of the total revenue, comes from individual income tax. The smallest sector, 8%, comes from sources listed as other. Individual income tax provides four and a half times as much income as corporate income tax Revenue Sources for the Federal Government

We determine this by finding the ratio of Individual Income Tax to Corporate Income Tax. From the circle graph we know this is 45:10, which is 4.5:1.

When a circle graph is presented , it is necessary to make statements about the sectors of the graph, relative to one another, and relative to the entire circle. From this one example, we can see the amount of information we can get, and all from looking at one circle graph! Now, let's try an example of reading a circle graph and answering specific questions about the data presented.