Pies for Binary Comparisons? Not so fast Skippy

If you study data visualization enough, you’re probably aware there is a large constituent of folks that believe pie charts suck. However, most have at least some level of acceptance for their use. ***although as I found out on Twitter last week, plenty of hardliners do exist***

Some experts say a pie chart should never exceed 5 slices, some say 3 and others say no more than 2. Personally, I’d say no more than 2…with a possible exception for 3 slices if you must.

Yet even if you only have only 2 slices, pie charts can still have their shortcomings.

While speaking with an industry expert some time ago, I shared a dashboard I had built. I had mistakenly thought hat using a series of pie charts would be a good choice to show the ratio between Red Badge and Blue Badge workers across 4 different regions. Needless to say, my colleague blasted this.

Here’s the reasoning. And it’s not that the pie charts don’t show the ratio well for each region…it’s the extra bit of insight that the pie charts can’t deliver…at least not very well.

Here’s what I originally had (I have omitted all labeling and axes as they’re not pertinent to this discussion & Red = Red Badge and Blue = Blue Badge in all visualizations):

While it’s easy to see the split of Red to Blue for any given region, it’s impossible to compare the regions. OK, may you be able look back and forth to see the slice..but which has more?

We could use size to show that right?

Sort of. But it’s been proven that we suck at comparing 2-D surfaces & Angles. What we do excel at is comparing length.

Using a bar graph, it’s easy to see  not only the ratio of red to blue, but also the total number for each region and how they compare to one another. And it takes up considerably less space! Very glad that someone pointed this out to me and hope you’ll find this valuable too!

I wrote about this one as I know that stacked bars have their shortcomings as well and I'm really hoping you will be vocal about what works even better!

Cheers, 

Kevin Taylor