After completing this unit, if you are given
a table of information that is to be displayed as a bar
graph, you should be able to:
- Identify the bar graph title.
- Identify labels for the bar graph axes.
- Identify information given by a designated bar.
- Determine the scale of a bar graph.
- Construct a bar graph.
Constructing Bar Graphs
Bar graphs are used to help visually represent data so that comparisons
and trends will be easier to see. In this section you will learn
how to construct bar graphs. We will begin with data presented
in a table. (NOTE: The procedure for constructing tables
was discussed in the Constructing Tables unit.) We will first
outline the elements of a bar graph and then the steps in constructing
Steps for Constructing a Bar Graph
Below are the steps to following when constructing a bar graph:
- Determine the following elements of
the bar graph from the table
- Title of the graph.
- Label for each axis--Here we
must determine which is to be the frequency
axis and which is to be the grouped
- Scale for each axis--Determine
the numerical scale for the frequency axis,
then the group names for grouped data
- Draw a set of axes that you will use
to construct your graph
- Determine which axis will
be the frequency axis--Determine whether bars will go
horizontally or vertically.
- Write in axes labels.
- For the frequency axis, determine the
- Use the data from the table to draw
in the bars on the graph.
Now let's go through the process of constructing a bar graph
using the table titled Student Housing at Union University.
Student Housing at Union University
Type of Housing
Number of Students
Off Campus Aparments
Off Campus Houses
- Determine the following elements
of the bar graph
- Title of the graph
--The title of the bar graph is the same as the title of the
table. The title of this graph will be Student Housing at Union College.
- Label for each axis--The
label for each axis comes from the column/row labels. In this
table the data is placed in columns, so we will use the column
labels. Once you know the axes labels, you need to determine
which is the frequency axis, and which is the grouped data axis.The
axes labels will be Type
of Housing, and Number
- Grouped Data Axis Label--This
is the axis that contains the groups. In this case it's the Type of Housing.
- Frequency Axis Label
--This is the axis that contains the frequency counts. In this
case it's the Number
- Scale of each axis--The
scale of each axis is determined by the data for each axis. Let's
look at each of these separately.
- Grouped Data Axis Label--Type
This data contains four groups. The data is nominal (not ordered)
so the groups could be placed in any order on the axis. The four
groups on the scale are: (1) Residence Halls,
(2) Fraternity/Sorority Houses, (3) Off Campus Apartments,
and (4) Off
- Frequency Axis Label--Number
As mentioned in the section on scale, the scale of the frequency
axis is determined by the range of the data. The data here range
from 985 to 3995. We can set the scale to run from 0 to 4000.
- Draw a set of axes that will you
will use to construct your graph
- Determine which axis
will be the frequency axis--Will
the bars be horizontal or vertical?
Determining which direction to construct the bars in is a matter
of preference. The information contained in the graph will not
be changed, but its visual appearance will be altered. In this
example we will place the frequency on the vertical axis.
- Write in axes labels--In
the first step we determined the axes labels were:
- The grouped data axis, which
is on the horizontal axis, is Type of Housing.
- The frequency axis, which is
on the vertical axis, is labeled
Number of Students.
- For the frequency axis, determine
the scale interval:
The interval of scale is the amount from one tick mark to
the next along the axis. If the range of the scale is small,
a general rule is to take the range of
the scale and divide it by 10. Make this your interval.
For ranges that are larger, the interval is typically 5, 10,
100, 500, 1000, etc. Use numbers that divide evenly into 100,
1000 (or their multiples)
in order to provide a graph that is easy to analyze.
In this case, if we take 4000 and divide it by 10 we get 400.
However, 500 is a number that is more easily analyzed, so we
will use 500. This provides a scale that is not too large and
easy to use in analyzing the data.
- Use the data from the table to draw
in the bars on the graph
Once we have the axes constructed, we are ready to draw in the
bars. Using the data from the table, draw in the bars to their
appropriate height. Keep in mind that this is somewhat of an
approximation since the scale does not make drawing exact heights
at Union University
While tables are more exact in their presentation of data,
they do not allow the quick visual view of the data. Bar
graphs provide one way to present data so that we can get an overview
at a glance. In the following practice you will construct
a bar graph. While you are doing this, think about the advantages
and disadvantages of both representations of data. (Comparison
of the different types of visual displays will be outlined in
the last instructional unit of this book.)