Visualizing Data: Six Hints on Using a Pie Chart

We are big fans data visualization (in addition to presenting data with numbers and tables). But even the basics of visualizing data can be challenging, so it is worth thinking about how and when to use some of the simplest tools, like pie charts and bar charts.

Pie charts can be particularly challenging because they are so common and so commonly misused.  When done poorly, they force us to think hard about what we are seeing and why.  When done well, they tell the story of our data.

Here are six tips on effectively designing and using pie charts:

• Pie charts are good for showing proportions, not quantities
• Use pie charts for category variables (like gender, or region) but not for variables that measure levels of things (like satisfaction)
• Pie charts should begin at 12 o’clock, and are read clockwise
• The maximum number of slices to the pie should be five or six
• Always show the numerical values on the chart
• Avoid three-dimensional “tilting” of the chart because it distorts true proportions

Many of us use programs and fancy tools that create charts automatically, all of which can be terrific tools. But keep in mind they will never replace the need for you to think about your story and how to portray it in a chart.

—Joe Hopper, Ph.D.