The Worst Chart In The World

Business Insider

The pie chart is easily the worst way to convey information ever developed in the history of data visualization. 

Sure, there are other more cumbersome ways to articulate data. But none have the credibility nor the widespread use that the pie chart has. 

Here, I'll explain exactly what's wrong with the pie chart and exactly why you need to stop using them as soon as possible. 

First let's talk about why we use charts in the first place. 

  • Charts are a way to take information and make it more understandable.
  • In general, the point of charts are to make it easier to compare different sets of data.
  • The more information a chart is able to convey without increasing complexity, the better.

I'll show you how pie charts fail most of these criteria for a good chart. 

The "point" of a pie chart is to show the relationship of parts out of a whole. 

Let's see how bad they are at the one thing they're ostensibly designed to do. 

Take a look at these three pie charts.

Let's say that they represent the polling from a local election with five candidates at three different points A, B, an C during an election:

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pie charts

Public Domain/ Wikipedia

 

So, what can we learn from this information?

Since these are the shares of the votes that each candidate will get, it should be easy for the reader to figure out what, exactly is going on in this race. 

But it really isn't.

In the first race, is candidate 5 doing better than candidate 3?

Who did better between time A and time B, candidate 2 or candidate 4?

Who has the most momentum in the race?

If the point of a chart is to make information more easily understandable, how is this chart working for you?

Indeed, were I to just give you a table of the polling values, wouldn't that be much easier to understand the information at first glance than these pie charts?

But now, let's look at that exact same information — parts of a whole — articulated on a bar chart:

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pie chart bar chart

Public Domain/ Wikipedia

Look at how much clearer that is. 

We can see exactly what is going on with each candidate at every point in the race at first glance. 

This bar chart is a much more clear indicator of parts of the whole than a pie chart, even when that's technically the point of the pie chart. 

Now let's look at another shortcoming of a pie chart, one that has to do with the way people don't really understand circles

Here's a pie chart of the party breakdown of the European parliament:

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Pie Chart European union

Walter Hickey / BI

So our main question is, can we really compare the slices to figure out the distinctions in size between each and every  pie slice?

If we're just trying to learn that, yeah, EPP is bigger than S&D, then what's the point of the chart? I could have told you that with two number. 

No, the chart is only useful if we're able to compare each and every element within it. 

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Pie Chart Exploded copy

Walter Hickey / BI

At right are the individual slices taken out of context for the purpose of comparison.

Look at them, and see if you can figure out an ordering from largest to smallest. 

The reality is, humans aren't very good at comparing slices of a circle when it comes to size.

It's the reason you probably found trigonometry and radians a lot more difficult than you found basic rectangle geometry.

That's not a bad thing, but it is something to keep in mind when trying to articulate information in the most comprehensive and understandable way possible. 

Here's that very same graph in bar chart form:

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Bar Chart European parliament

Walter Hickey / BI

Notice how you can compare each and every party to each and every other party. 

You're just comparing the length of rectangles in order to understand what's going on. 

If you really wanted to, you could even change the left axis to percents to figure out the different allocations within parliament. However, now you're able to see how many seats each party holds, information that wasn't present on the initial pie chart. 

Now, let's look at how easily pie charts can be manipulated. 

Here's that same data as above, only on a 3D Pie Chart:

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3d pie

Walter Hickey / BI

People do this all the time, and that's because an angled 3D pie chart is an excellent way to lie to you. 

Looking at this chart, S&D — the red party — appears to be roughly even with EPP, the teal party.

But the reality is, that's because I've distorted you perspective to make it seem as if red is in fact bigger. 

This is so easy to do, and it's honestly a shame that Excel makes it possible to begin with. 


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Red Green Colorblindness

Walter Hickey / BI

At left you'll see another example of the shortcomings of the pie chart. 

The fact is, 10% of the men reading this will have no idea what we're talking about. 

The most elegant charts don't require data labeling.

You shouldn't need to have any extraneous numbers on your data in order to make your point.

If you do, you are using the wrong chart. 

Oftentimes, the pie chart is the wrong chart

So, let's review:

  • Whenever there is similarity in the information available, a pie chart is not the right chart to use.
  • Whenever there are multiple (3 or more) different points of data, a pie chart is not the right chart to use.
  • Pie charts are very easy to abuse. 
  • A pie chart is not the right chart to use if you need to  label each percent. 


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detroit property tax delinquency

Business Insider, data from City of Detroit

Before we look at a final critique of pie charts, let's acknowledge that there is something they're actually good at. 

The one single thing pie charts are good at is when you're comparing 2-3 different data points with very different amounts of information. 

That's it. 

And when you get down to it, if that's the only they're good for, their only real use is to let people know what a fraction looks like. 

The only point of the pie chart to the right is to inform people what 32 out of 100 looks like. 

Last week I made the comment that pie charts are the Nickelback of data visualization. That comment got a lot of circulation. 

But after thinking about it, there's a much more apt metaphor. 

Pie charts are the Aquaman of data visualization. 

Aquaman is really only good at one thing. Even so, other DC superheroes can often do Aquaman's job better than Aquaman. Superman can hold his breath underwater, Batman has his submarine. It's come to the point where if there's a sinking oil tanker, who do you really want to call? Aquaman? Or Superman?

You sort of always wonder why Aquaman was invited to the meeting in the first place. 

And when that one real chance for Aquaman or the pie chart comes around — maybe you need to talk to a fish or explain what 32% looks like on a circle — you're sort of left to wonder why you actually bothered having it around in the first place.

In short, stop using pie charts. They're not useful, they're too easy to screw up, and they don't accomplish the one thing you actually use charts for — to make information visually informative. Pie charts are Aquaman. 

So what should you do instead?

As Edward Tufte — a data scientist who has written extensively on the failure of the pie chart — tweeted:

Pie chart users deserve same suspicion+skepticism as those who mix up its/it's, there/their.To compare,use little table, sentence, not pies.

— Edward Tufte (@EdwardTufte) January 10, 2013

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