A dot plot, also known as a strip plot or dot chart, is a simple form of data visualization that consists of data points plotted as dots on a graph with an x- and y-axis. These types of charts are used to graphically depict certain data trends or groupings. The most famous dot plot is perhaps the Federal Reserve’s projections for interest rates that are published each quarter.
A dot plot is similar to a histogram in that it displays the number of data points that fall into each category or value on the axis, thus showing the distribution of a set of data.
A dot plot visually groups the number of data points in a data set based on the value of each point. This gives a visual depiction of the distribution of the data, similar to a histogram or probability distribution function. Dot plots allow a quick visual analysis of the data to detect the central tendency, dispersion, skewness, and modality of the data.
Dot plots are typically arranged with one axis showing the range of values or categories along which the data points are grouped and a second axis showing the number of data points in each group. Dots may be vertically or horizontally stacked to show how many are in each group for easy visual comparison.
This is not unlike a line graph. The big difference is that dots on a dot plot are not connected via a line. However, line graphs connect the dots with a line. The line graph, like a dot plot, has both an x-axis and y-axis.
Dot plots work best for smaller data sets, as the number of dots can become less manageable with larger data sets.
The key dot plot types are the Cleveland and Wilkinson dot plots. Both utilize dots, however, there are key differences, where Cleveland is akin to a bar graph and Wilkinson is more like a histogram.
The Cleveland dot plot lists the variable as continuous, versus a categorical variable. This is akin to a bar chart, but unlike a bar chart—which uses length to relay position—Cleveland dot plots use position. William S. Cleveland created the notion of a continuous variable in his book “Elements of Graphing Data.” The Cleveland dot plot is useful when using multiple variables, as it does not require the axis to start at zero, allowing for the use of a log axis.
The Wilkinson dot plot lays out data much like a histogram. It has individual data points, whereas a histogram lays out the data in bins. The Wilkinson dot plot was created by Leland Wilkinson, which helps standardize the dot plot form.