Monday, March 29, 2010

Pie Chart Defense!

In the world of statistics and data visualization, you often find a backlash against the simple pie chart. Here at the playfairgroup, this discussion comes up quite a bit. Our point of view? The pie chart can be great when it is exactly that - SIMPLE.

Mike's story:
So I was chatting with a friend of mine on Skype last night and I was
going into some detail about my affinity for pie charts.
He simply responded:
"Pareto and histogram. Everything else is bullshit"

Dan's visual response:

Can’t put a histogram on a map! (at least not in Tableau)

Catherine's response:

First, histograms are only good for certain situations (a lot of data points, when you are trying to see the overall distribution, etc.). But, since they data is put into categories, it is easily manipulated based on what categories you pick (like ignoring the differences between months when grouping data into a full year). Pareto charts have a lot of the same problems.

Is your friend in QA? He's probably following the 7 useful charts that exist according to QA Wikipedia:

As I've said before, pie charts are very effective for certain situations. It's for a general estimate of ratios, not exact percentages (that's why I always label them!). I usually only like a few slices max, because it starts to get misleading if you are looking at similarly sized pieces (since it's not obvious which is bigger). But showing that this group is 10% of the whole, this other group is 20% of the whole, and 70% other? Well that's what a pie chart is made for!!

Tell your friend to put THAT in a histogram!!!!!

And, with final thoughts, Dan:

Here's a couple articles in defense of pie charts if you ever need ammo to support your love of pie charts:

“I don't accept the information design dogma that pie charts should never be used. Pie charts have weaknesses but they also have many strengths. Put them back in your bag of tools and pull them out when appropriate.”

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