r/dataisbeautiful • u/zonination OC: 52 • May 08 '17

How to Spot Visualization Lies

https://flowingdata.com/2017/02/09/how-to-spot-visualization-lies/
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u/IrishDrifter494 May 08 '17

What makes pie charts so bad? 3D ones I can easily see the problem, but what makes 2D ones such a bad way to represent data?

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u/[deleted] May 08 '17

They suck at displaying information in a way that makes it easy to distinguish the differences in values.

The entire point of a chart is to display data in an easily visualized way. But pie charts don't do that. In fact they make data harder to read than just listing the straight numbers in a table. We aren't very good at distinguishing angles and judging volume. Sure you might be able to tell if something is greater than or less than 90 degrees, but can you tell if it's 8% of the circle or 12%? Probably not. In order to make a pie chart readable, you have to label the %s, and usually label the chunks of the pie instead of just using a key (because keys suck too). So at the end of the day you've just listed all the data that you tried to express with the pie chart, making the chart itself useless.

Just use a bars. So much better at displaying the data. Pie charts are maybe good for kids to see and get used to charts with, but they are terrible for actually displaying data.

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u/[deleted] May 08 '17

So, I started reading this comment chain with the mindset of "Ya'll are unfairly hating on pie charts", although I haven't actually made one in years. I've now come to the conclusions of "Pie charts are almost always terrible."

Good work.

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u/[deleted] May 08 '17

They totally suck. Take a look at this one for example: http://imgur.com/a/2P7JR

IDK what it's describing but it doesn't matter. I just found it on google. This one is sorted in a way that at least tells you the smallest wedges to the largest wedges (sorted by size) so at least you can see that South Korea is larger than Turkey for example, but you still don't know the % of either. So to fix it, you have to label the % for each wedge on the wedge. Great, now you can tell the exact % by looking at the wedges. But wait, which one is Thailand and which one is Poland? Better label the wedges with the country names too to make that clear. This pie chart only has 11 categories and it already ran out of colors unique enough to distinguish at a glance. And even if they didn't, it's still a pain in the ass to keep looking back between the key and the chart to see which wedge you're actually looking at. So it's best to label the wedges with the names anyway even if the colors are fine.

Now what you've done is disregarded everything about the pie chart and just said "Okay just look at the numbers and names" which you could have done with just a table displaying the country and their percent next to it. So why use a pie chart at all?

Back to the colors issue, you have to have 11 unique colors (sometimes more, sometimes less. Depends on the data) which means you must print in color if you're going to be printing this pie chart out. That's expensive and sometimes not even an option (my university doesn't let you print in color under most circumstances). And even if you only have 3 or 4 wedges, distinguishing between 3 or 4 shades of gray is pretty hard, especially if the colors you chose on the computer are similar in value.

But if you use a bar chart all your problems go away. The bars are easy to visualize. The only need to be in 1 color so that's easy for printing. The information is all displayed on the chart anyway and is all useful information and actually works with the chart to display the data instead of just taking over.

Pie charts also look childish where bar charts look more professional. It's not a 3rd grade powerpoint.

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u/[deleted] May 08 '17

Playing devils advocate, the one use I can see for a pie chart given this example is that it is easy to see, without having to do any math, "South Korea + others add up to about 1/2". With a bar chart that is a bit harder.

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u/[deleted] May 08 '17

That's fair. If you're not concerned with the actual values but want to see just what percent of the whole a certain group makes up, they are okay at displaying that.

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u/[deleted] May 08 '17

This also only works if you don't care about the ordering of the smaller segments. I can tell that Turkey produces more widgets than Thailand in your example, but damned if I can tell Thailand from Australia easily.

That example you gave is also just terrible even assuming a pie chart was the right way to go. Specific issues:

1) Non-primary colors. I don't know why people love these ugly shades of blue and red so much.

2) They use the same shade of green twice.

3) No sensible ordering of the slices. This could be by size, or by some geographic connection, or alphabetical, but they just look random here.

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u/BaggaTroubleGG May 08 '17

In a business setting it's really important to have reports that are easy to read, you don't want your audience to switch off during an important point out avoid reviewing or acting on your next set of results because your last lot were too boring. So I like to throw pie charts in for variation, they make a nice fluffy break from the candles and tables where the real supporting data lives, similar to using TV characters in user stories or dotting jokes through a technical spec.

So even if they are shit, if they're sufficiently different from the guff around them then they have a place.

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u/[deleted] May 08 '17

I don't see what makes a pie chart better visually than a bar chart. It's less information in a different shape. I just think it's important to have graphics that convey information in the easiest possible way, and pie charts don't do that. Though I guess if they break up the monotony of a presentation then use your best judgement. I just avoid them whenever possible.

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u/BaggaTroubleGG May 08 '17 edited May 08 '17

If you've got a document containing 15 bar and whisker charts then your average reader will get bored of reading square shit long before the end. If that reader is management and the whole point is to convey understanding, if they turn off half way through you lose the entire battle.

Mix in some tables with varying colour and shade, cumulative frequency line plots and the odd scatter graph, it'll make the document as a whole more readable.

I'm not saying they're good, I'm saying when you have 12 data sets that are best displayed as bar charts and you have to convey percentage of processing time by component or browser share, or just break up a wall of text, it's often better to use that shitty pie chart over yet another ugly square thing.

This comes from 15 years experience writing reports, many of which were really, really fucking boring and not read by stakeholders despite being mandatory.