Pie Charts are usually a bad idea

Pie charts are usually a bad idea. Although they superficially appear to be a way of expressing data visually, in reality they depend heavily on the labels and values to make any sense. Once a pie chart moves past about 3 elements it becomes very difficult to judge the different values, by the size of the sectors, especially if two sectors of interest are not adjacent. And, don't let me begin to start ranting about using two or more pie charts and then challenging the reader to draw an inference!

I suspect that the popularity of pie charts has something to do with the enthusiastic way they are taught in our schools. For teachers pie charts allow simple data to be combined with practice using angles and protractors. This makes for a great bit of teaching, but leads us to the impression that pie charts are useful.

A recent post on Junk Charts has a great example of the problems that real data create when people try to illustrate them with pie charts.

Comments

[Jared]

I tend to stick to two elements, unless there a big differences between the three elements.

[LoveStats]

We're on the same page! I did a blog on pie charts and included a sample chart where 3 separate slices are the exact same number but appear completely different. That always surprises people!