Pie Charts – how not to use them!

I originally posted this to my LinkedIn Profile, which you can find here, but thought I’d share it on here as well!

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Plenty has been said before about whether or not you should use Pie Charts to present your data.

A good article covering their main pitfalls can be found here;

and a slightly lighter take on them can be found here;

Yet, it was my own father who reminded me that Pie Charts can be put to good use, as was the case with Florence Nightingale. (Though, they were of the somewhat more useful Rose Diagram type than bog standard Pie chart, but I take the point!)

Having said that, I came across this little gem, on the BBC news website of all places, which really must be the single worst usage of Pie Charts I’ve ever come across

If nothing else, it’s clear what it’s trying to show you – but fails miserably on delivery. The chart – whether viewed in isolation (without the legend), or even with the legend, offers absolutely no insight whatsoever. Without looking at the legend, what do we know? Who scored the most? How many goals was that? What margin is there between the top & ‘bottom’ top scorer? Nope, nothing.

And what does the ‘total’ pie represent? All goals all time? Nope – just those of a few select players. Pie segments should at the very least be a ‘contribution to a total x’ representation. Oh, and who is ‘Own Goals’? – it’s utter nonsense.

I’d suggest that the only way it could be less useful would be for all the segments to be the same colour, but you know what? I actually think it would help – at least that way the message would be ‘they’re all about the same’.

So please, if you think you have a valid use-case for a Pie Chart – get a second opinion before you go ahead with it, and ask yourself ‘what insight does it give me that I wouldn’t otherwise get’.

On a lighter note, this pie chart landed in my mailbox the other day, and is actually quite a decent use of a pie chart – highlighting an extreme set of values where you wouldn’t expect to see them, and is also a ‘contribution to a total’ chart, so makes a lot more sense.

UPDATE:

I’ve been trying to find a link to the original article. It was related to Wayne Rooney’s goal scoring record. I struggled to identify exactly which article it was, but it does seem they saw sense and removed the pie chart, replacing it instead with this;

Which is a far superior representation of the data – not perfect (difficult to see who has the highest value – why show the values below the chart when you could cleanly display them as labels on the chart?)

And in fact, there’s now another set of pie charts in the same article, which actually works reasonably well, showing the relative makeup of each person’s goal record; we can quickly see what Rooney scored most of his goals in competitive matches, whereas Bobby Charlton and Jimmy Greaves scored most of theirs in friendlies.

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