Dot plots encode single data points with circles, often on a line.
While a bar on a bar chart consumes a lot of space in order to represent a single number, a dot in a dot plot simply represents the single number. Comparisons are easily made by plotting more than one dot per line, such as pretest scores and posttest scores. According to prominent data visualisation scholars, dots on a line is the easiest graph type for people to interpret.
Test score differences between fall and spring over 5 subject areas
This example depicts fall and spring test scores in 5 subject areas. Each score is represented by a dot. Each subject area is on its own line. The dots run in order of least to greatest by the spring scores.
Source: Stephanie Evergreen.
Advice for choosing this method
Dot plots are handy for comparing between 2-4 points on a line. If you have more than 4 points, the dot plot will likely get too cluttered. If you have points that are very close together, the dots will overlap one another and could be difficult to interpret unless you forego direct number labeling and make each dot empty or transparent.
Advice for using this method
Order the categories in some logical way. In the example above, they are ordered least to greatest according to the Spring test scores. Another way to order could be by the most change that has occurred, such as is shown in this report (pdf - jump to page 22 for a good example).
Other ways to compare sets of values
'Dot plot' is referenced in:
- Rainbow Framework :