Figure 1. Example of a dot plot
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A dot plot is a chart that shows a dot for each observation on a single scale. An example of a dot-plot is shown in Figure 1.
Figure 1. Example of a dot plot
The figure shows that four people had two drinks. Note that there is no need for a vertical axis (although one could be added for convenience). Although sometimes a dot-plot could refer to a scatterplot one definition of a dot-plot used in this reader is shown in the box below.
| Dot plot Diagram where each score is represented by a dot. |
An alternative version of a dot plot is a so-called Cleveland dot plot. Only the top dot is shown, as shown in the example in Figure 2.
Figure 2. Example of a Cleveland dot plot.
In a Cleveland dot plot a vertical scale is required.
| Cleveland Dot plot Dot plot where only the top dot is shown and a vertical scale is added. |
Although a vertical scale is added, less dots are used. The overall amount of ink required will usually be less.
When creating a dot plot for a continuous variable the width of the dot can be considered the class width (unless you allow for overlapping dots). Since the class width are then all equal each dot can represent one case (i.e. the absolute frequency is used and not the frequency density).
If you are interested in more details about dot plots, Wilkinson (1999) wrote a nice article about them.