Constructing
Bar Graphs with
Negative Frequency Values
The steps for constructing a bar graph, as outlined in the
unit Constructing Bar Graphs,
are:
- 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
data axis.
- Scale for each axis--Determine
the numerical scale for the frequency axis,
then the group names for grouped data axis.
- 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
scale interval.
- Use the data from the table to draw
in the bars on the graph.
When constructing a bar graph with negative
values, you follow the steps above, paying close attention to
the scale of the frequency axis. Since there are negative
values, the scale of this axis will not start at zero. Let's use
the table on the previous page to illustrate this. Since this
process was described in detail in the last unit, we will focus
on the frequency scale construction here.
- Determine the following elements
of the bar graph from the table
- Title of the graph--Net
Exports of Selected Nations.
- Label for each axis--
Grouped Data Axis Label--Country
Frequency Axis Label--Net Exports (billions
of dollars)
- Scale for each axis--The
scale of each axis is determined by the data for each axis.
Grouped Data Axis Label--Country
The data has six groups and is nominal data. The six groups are:
(1) Canada,
(2) France, (3)
Italy, (4) Japan,
(5)
Britain, and (6)
US.
Frequency Axis Label--Net Exports (billions of dollars)
If you look at the table, the data frequencies range from -132
to 142. Since we have negative values we must have a scale that
can incorporate these. Setting the scale to run from -150 to
150 is an appropriate choice for the scale because it incorporates
all the values.
- Draw a set of axes that you will
use to construct your graph
- Determine which axis
will be the frequency axis--Let's use the horizontal
axis for the frequency, and vertical axis for the grouped data.
- Write in axes labels (see
below)
- For the frequency axis, determine
the scale interval--Recall that our general rule is
to divide the scale by ten to obtain an interval of scale. This
will give us a starting point from which to base our interval
of scale. When there is another interval of scale which makes
sense or is more convenient, choose that interval.
The scale is from -150 to 150, which is a range of 300, so our
interval of scale could be around 30. The choice of 25 works
well, so choose that interval.
Net Exports of
Selected Nations
One thing you should notice about the frequency scale is that,
while it does run from -150 to 150, the axes intersect at the
zero on the frequency axis. This provides us with positive and
negative regions for drawing in the bars.
- Use the data from the table to draw
in the bars on the graph.
As mentioned above, the bars are drawn, beginning at zero on
the frequency axis.
Net Exports of
Selected Nations
