Graphing Guidelines
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A large percentage of people find reading graphs difficult, so you should make your graphs as clear as possible for their sake. The advantage of this is that everyone else will find that your graphs easier to understand. The following are some rules of thumb for creating graphs. As you create more and more graphs, you will gain a better understanding of what works and what doesn't, and you can modify these guidelines accordingly.
Present the data
clearly. |
Start frequency and relative frequency scales at zero. If you have a choice, choose bigger graphs over smaller graphs. |
Focus on the data. |
With the exception of frequency scales, numeric scales should extend from the minimum data value to the maximum data value but not much farther. |
Provide explanations as needed. |
Add titles to graphs, label axes, and identify different data groups clearly if there are more than one. |
Avoid distracting details |
DON'T use 3D bar charts or 3D pie charts. While the three-dimensional look of 3D bar charts and 3D pie charts may intrigue the viewer, 3D bar chars and 3D pie chats are more difficult to interpret than the 2D varieties. Also, do not code different data groups with letters or numbers when descriptive names for each group could be used instead |
Examples of Good and Bad
Bar Charts
Figure 1: GOOD Bar
Chart
Figure 2: BAD Bar
Chart
The frequency scale on this bar chart goes too far up. As a result, the chart does not focus on the data. The horizontal lines here are marked at multiples of 50, but since there is no bar above 150, there is no reason to go above 150. Notice how the bars in Figure 1 are twice as tall as those in Figure 2, even though both graphs are about the same size.
Figure 4: BAD Bar
Chart
This is called a 3D bar chart. Because of the way the bars are drawn, they
look like they are three dimensional.
Unfortunately, drawing the bars this way, makes the chart more difficult
to interpret. In this chart, it looks like the
frequency for
Graphing Rules for this Class
For the graphs you create in this class, you will be expected to label and apply scales to the axes of all graphs on tests and assignments. The numeric scales must be uniform. This means that if on one axis, the distance from zero to one is one-centimeter, then any other one-centimeter distance on that axis should represent one unit. The other axis may have a different scale. Always use tick marks to show the location of numeric values on numeric scales. All frequency scales or relative frequency scales must start at zero. Finally, use a ruler when drawing graphs. Failure to do any of these things may cost you points.