I think the time has come for the formation of a new organization: Citizens Against Pie Charts. I have no idea why the media seem so addicted to them – because quite often they’re eminently unsuited to their apparent task, to show the relation among various quantities of related items. And that is because people really are not good at determining relative scale between two “pieces of pie” at odd radial angles within a pie chart. A pie chart does one thing well: it shows that the various components of whatever it’s measuring add up to a whole. How often is that really what needs to be known? A lot less often than pie charts are used. Probably nine times out of ten when you see a pie chart, a column graph would convey the desired information far more clearly and cleanly. But America’s infographics editors have a smutty passion for the pie chart – and so its pointless reign in newspapers, business reports, and websites continues.
Here, for example, is a pie chart showing the relation among six different items. I chose the quantities somewhat arbitrarily, only making sure that some of them were rather close.
Which is larger: quantity 4, or quantity 5? Is the sum of quantities 2 and 3 larger than quantity 1? Pretty damned hard to tell, isn’t it.
Now try answering the same questions, this time looking at a column graph built from the same data:
Much easier, isn’t it? And if I’d wanted to, I could have color-coded those columns (I blame Excel) to make the graph a bit more interesting and the distinction among the various items more clear.
If for some reason it was also necessary to see how those items parsed out as a proportion of the whole, why not put small pie charts, each one oriented with its particular quantity’s left margin straight up and down, at the bottom of each column, to show the way each item fits into the overall numbers? The graphic would be more complicated, but still much clearer than the pie chart.