Here is another tip in a series of tips on different chart types. The idea is to fill up your toolbox with an array of charts good for making sense of data. This week, I give you the parallel coordinates plot.
Active Ingredients (What is a parallel coordinates plot?)
Parallel coordinates plots look kind of like the electrical poles and wires along the highway. They are a series of axes (that’s the pole part) connected by various lines (that’s the wire part). Each axis represents a variable that you can measure numerically. Each line represents an individual unit, group, or category. For example, each line might be program that your organization offers. And one axis might be enrollment, another axis drop out rate, and another average rating on participant surveys. You can compare programs by seeing where each line hits each axis.
Uses
Parallel coordinate plots are great when you have a lot of measures and want to compare a bunch of individual units, groups, or categories on those measures. In the example below, each axis represents a different chronic illness and each line represents a state in the U.S. So we can see that the percent of adults with kidney disease is much lower than the percent of adults with arthritis across states. But we can also see where there is variation among states. For example, Oregon has a much larger percent of adults with depression than does Hawaii. The line for Hawaii is highlighted to allow the viewer to compare Hawaii to other states on various chronic illnesses. Note that in this example, each axis uses the same scale (percent of adults) but in some parallel coordinate plots, each axis has a different scale depending on the unit of measure appropriate for each variable.
Warnings
The order of the axes will affect how the data is perceived. In the example, I ordered the axes from diseases with relatively low prevalence to those with relatively high prevalence to allow the viewer to easily distinguish diseases in this way.
Parallel coordinate plots can get cluttered fast. You can avoid this by limiting the number of lines or axes or by greying out most of them and highlighting just one or two as in the example above.
Fun Fact
Parallel coordinates plots go way back, to at least the 1880s when Henry Gannett and Fletcher Hewes published one in the Statistical Atlas of the United States. Check out their parallel coordinates plot which shows the ranks of states on a wide range of issues in 1880 including populations density (DC ranked number 1), per capita wealth (California ranked number 1), and literacy rate (Wyoming ranked number 1).
To see past data tips, including those about other chart types, click HERE.
Let’s talk about YOUR data!
Got the feeling that you and your colleagues would use your data more effectively if you could see it better? Data Viz for Nonprofits (DVN) can help you get the ball rolling with an interactive data dashboard and beautiful charts, maps, and graphs for your next presentation, report, proposal, or webpage. Through a short-term consultation, we can help you to clarify the questions you want to answer and goals you want to track. DVN then visualizes your data to address those questions and track those goals.
