Why are pie charts so controversial?


(Jennifer Looi) #1

Bashing pie charts seems to be a common topic of conversation to bond over for data geeks - like complaining about public transit or traffic for the rest of us. Why all the hate? Although there seems to be at least one pie chart in every report or newspaper you read, they actually have a much narrower range of use than we’d expect. Pie charts can be effective for high level takeaways involving a couple of categories, like in comparing % of respondents who said yes vs no. In cases like this we probably don’t care so much that 51% voted yes and 49% voted no, but about whether people responded yes significantly more, less, or about even as the others.

However, once we start caring too much about what that percentage breakdown is, or throw in another section (like % maybe), it’s a lot harder to get that information at first glance. Then, pie charts start generating questions like is that 27% or 29%? Are those all about a third? Or is one at 40% and another at 30%? At that point, most people would be better off with something like a bar chart. For a nice visual explanation of this, check out this article.

(MDuiker) #2

Hey @JLooi, bar charts seem to always be a dependable backup plan but never my first choice.

I have 2 questions for you:

  1. Is there anything bar charts can’t do?
  2. When are bar charts the best option?

(Jennifer Looi) #3

Great questions @MDuiker! Bar charts are by no means one size fits all, but variations of bar and column charts do tend to hit the widest range of uses for the average person. The most important factor is purpose: am I trying to show a relationship/correlation between two things? Or just a comparison? Or something else? In my experience, the two biggest weak spots for bar charts (and their variants) are for showing correlations: a scatter plot or line chart is easier to follow. Distributions, like showing a normal curve, can also be a weak point although histograms are pretty visually similar and can generally work as an alternative.

I find this resource helpful for getting started in the right direction, although the suggestions are guidelines rather than hard and fast rules. There’s also an old, but good article by Lifehacker that outlines purposes and best practices here. Hope this is helpful!

(Stacey McDonald) #4

FYI - One of the reasons that bar charts are a great option is that they are so easy to read (for our brain). People have an easier time comparing the length of the different bars, then say comparing colour or area.

Here’s a great article about how to use pie charts correctly by Datawrapper.