More On Pie Charts

A few days ago, I posted a link to the Skeptical Optimist (i.e., Steve Conover), and referred to one of his charts as a "bad pie chart." Steve took exception to my characterization, and posted an update:

I usually ignore nitpicking, but I'll make an exception in this case. Excel expert John Walkenbach has judged this to be a "bad" chart, because, as he explained to me, "a bar chart would convey the information much better."

Well, John and I will just have to agree to disagree on this. Here's one of many links to explanations of which chart types to choose when. Not sure if John has seen it, or one like it, but it's a concise summary.

The shares of the federal debt owned by various entities as of Jan. 2007 call for a pie chart. It's a snapshot in time, and it's a compact representation of all the portions (unlike a bar or column chart that's spread out vertically or horizontally).

In my judgment, this chart makes it much faster and easier to check the facts against the political rhetoric. John disagrees. So be it.

I'm not aware of any generally accepted standards for charts, but I still think his pie chart is way too busy.

So I spent some time trying to come up with something better. Here's my first attempt, a bar chart (click to see a large version).

This chart conveys the same information and is a lot less "busy." But I still wasn't satisfied. All of those tiny data points left too much white space. So I tried another chart type -- something that Excel calls a bar-of-pie chart. It's a pie chart, but it allows some of the little pieces to be broken out into a vertical bar chart.

This chart is still rather busy, but I think it conveys the point fairly well -- and avoids having too many slices in a single pie. Rather than identify each tiny little bar component, I added a text box that lists them. My feeling is that nobody really needs to know which bar is associated with which country, and the main point of the chart is not lost. The data labels show percentages (rather than values), but it would be easy enough to show the actual values if necessary.

I've always enjoyed playing around with charts, and this particular set of data presents a challenge because of the large number of data points with small values. I'm not saying that my chart is the ultimate solution, but I do think it's a much cleaner way to make the point.

I think I'll use an example like this in my Excel 2007 Charts book. It would be nice to use the original chart, but that would require Steve's permission.

If anyone would like to try making a better chart, here's an Excel file with the data.