Some critics have come crashing down hard on pie charts. Edward Tufte says “the only thing worse than a pie chart is several of them.” Stephen Few says “save the pies for dessert“. Cole Nussbaumer says “Death to pie charts.”
Well, they are all wrong. Pie charts deserve your respect. And I’ll tell you why.
First, let’s consider the critics’ valid criticisms:
1. A bar chart allows more accurate comparison than slices in a pie chart
This is true. But not every chart is about making precise comparisons. Sometimes you only need approximate values so you can engage in a discussion. It’s not necessary to see that one slice is 1% larger than another slice to have that discussion.
For instance, take this pie chart from Stephen Few’s article. Clearly, a bar chart gives more precise comparisons.
But what if, instead, the only point you want to make is that the 2 largest distributors control 65% of the market. Which graph demonstrates that more clearly?
Few admits there is research (Spence and Stephan Lewandowky, 1991) demonstrating pie charts are superior in this case, but he assumes this is a very “rare in the real world”. On the contrary – this is extremely common in business presentations where the goal is to tee up issues for discussion, not just lay out the data for detailed study and comparison.
In fact, if you sort your pie slices from largest to smallest, you don’t need to depend on visual comparisons. The ordering tells you which is larger, right?
2. A line chart shows trends more clearly than side by side pie charts
Again, this is often true. But it depends on the data you have, as well as the impact you want on the audience. Certainly a pie chart with 10 slices is difficult to compare over time. But what about a pie with just 2 slices?
Tufte’s dogma often unravels when you press on it just a little. He argues you cannot accurately see trends when you compare pie charts side by side. In fact, pie charts CAN be a better way to visualize side by side data when the data is simple. And when you’re comparing percentages, bars are NOT more accurate than pie charts. Look at these two displays. Which one communicates more quickly?
In this case, a pie chart is not hard to compare. But what about a line graph? Certainly, it does the job. But there’s also a bit of confusion. Because we are referring to 3 separate events and how they differ. A line graph communicates a smooth continuation of changes throughout the day. That isn’t quite what we are saying and so it takes a bit of mental gymnastics for the reader to adjust the line graph to its intended meaning. The criss-crossing lines also introduce a bix of complexity.
In fact, despite some of the valid reasons to avoid pie charts, there are also valid reasons pie charts can be SUPERIOR to line charts and bar charts:
1. Puts the audience in a positive frame of mind
Perhaps most importantly, the visual system LIKES round things more than sharp angles. Research finds our emotions are more positive to rounded corners than sharp corners. No matter how accurate your data, you cannot deny bar charts are just BORING to look at. Or, at least, more boring than pie charts.
Some in the hard-core scientific community do not recognize emotion as a valid reason to use pie charts. That’s understandable given their mission of presenting data truthfully and accurately.
But great presenters have a different mission: to simplify ideas and motivate audiences. And they know that precise logic and measurements are not enough; you also have to appeal to them emotionally. Pie charts help put the audience in a positive frame of mind.
2. Communicates part-to-whole relationship better
At a glance, you know a pie chart is splitting a population into parts.
Bar charts do not have the same meaning. You can signal to the reader the bars add up to 100%, by adding a column or an annotation. But this requires some extra mental gymnastics by the reader to understand the bar chart represents 100%. Nothing beats a pie chart for instantly communicating 100%.
3. Easier to estimate percentages
Research shows that it’s easier to estimate the percentage value of a pie chart compared to a bar chart. That’s because pies have an invisible scale with 25%, 50%, 75% and 100% built in at four points of the circle. And the angle of the pie’s interior corner provides an additional cue not available in unlabeled bar charts.
Especially as pie charts become smaller, and you need to use a lot of them, pie charts can communicate percentages much more quickly than bar graphs. See for yourself. (here’s another example)
Tufte is wrong to make an assertion about pie charts based on his own context (the analysis and presentation of complex data) and use broad strokes to apply that to domains where he has no expertise (presenting and selling ideas in the boardroom). Pie charts have earned their place in your business presentations.
So, take some advice from someone who presents data to executives. Use pie charts
- When you want to affect your audience emotionally
- When you want to quickly communicate a part-to-whole relationship
- When approximate values are enough to have a productive discussion
And my advice to Tufte? Pick up a copy of my new book, tentatively titled “Storytelling with Graphs” for a more balanced and practical view of the role of graphs in visual communication. I’m hoping to have it released this summer.
About the author: Bruce Gabrielle is author of Speaking PowerPoint: the New Language of Business, showing a 12-step method for creating clearer and more persuasive PowerPoint slides for boardroom presentations. Subscribe to this blog or join my LinkedIn group to get new posts sent to your inbox.