Pie Charts – Our Evil Friend


Everyone who knows me knows I hate pie charts. How could I, you ask, hate such a beautiful visualization of percentage data? Well, i just outright request that people not use pie charts because the charts are often taken far beyond their intent. All of our new and fabulous software allows even the most unskilled person to create amazing charts. And sometimes, or most times, they’re made into 3D, rotating, florescent monstrosities.
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The purpose of a pie chart is to clearly display relative percentages. The intent is to be able to quickly determine that one slice of the pie is slightly bigger or slightly smaller than another slice. When a chart has been tilted for dramatic effects, the slices become skewed. I’ve even gone so far as to run (non-probability, convenience sample) tests to see how people interpret 3D pie charts. What I found is that people are unable to determine which slice is the bigger slice! In fact, if you look at the picture here, you’ll various slices, each representing a proportion. What you don’t see, though, is that THREE of the slices in fact represent the exact same proportion. Three of them are 11%, one is 22% and one is 44%. Unless your job requires you to misrepresent data, this is certainly not the way to go.
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And that is why I hate pie charts!
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  • 6 responses

    1. I believe that John Tukey made the observation.

      “There is no data that can be displayed in a pie chart, that cannot be displayed BETTER in some other type of chart.”

      http://en.wikipedia.org/wiki/John_Tukey#Quotes

      It sounds like you are in good company.

    2. […] no expert in graphic design or data visualizations.  I do know that pie charts are evil, as are most gauges and uses of 3D in dashboards.   However, when I saw this bar chart […]

    3. Actually I think in the pictured Pie0chart here it’s still quite clear. But I do think that ‘on a professional level’ we wouldn’t want to see any distortions of the parts, regardless of how ‘bad’ or not it looks in one particular case. So I agree with the perspective argument. Why anyone would then use a pie-chart on a ‘non-professional’ level is beyond me, I’d rather take a nice flower as a colourful illustration, so in the end I can’t think of any proper use of a 3D pie-chart.😉

      I figure it’s a common thing to tinker with the visual representation if you didn’t have time to make data up to suit your needs. (Think about the common cutting off of bar-graphs, as to increase the perceived differences) So I wouldn’t go as far as “ban all of the pie-charts” but I’m more of a “think twice about what you’re actually seeing, ALL the time”.

    4. Wow. You’re definitely right about the skewed perspective, I’ve never realized it before – they just look pretty and you want to use them (doesn’t hurt that my boss likes them). Is it only 3D pie charts that you’re against, or all pie charts? You start off saying you hate pie charts, but then explain its the skewed look… Didn’t know if there were more reasons not to use a pie chart

      1. 🙂 I say all pie charts for two reasons. 1) The skewed nature of 3d and people can’t resist 3D. On that note, any chart in 3D just isn’t a good idea for the exact same reason. You can never really read the number it is supposed to represent. 2) People forget that a pie is supposed to represent percents and they throw anything into them. it’s just easier to say all pie charts.

        Most people love 3D. I agree it’s pretty but let’s save 3D for great movies like ‘UP’!

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