I’m settled at my new job, and I’m looking forward to getting back to this blog now and then. I plan to feature critiques in the form of “Hall of Shame” and “Hall of Fame” examples of visualization each month. I hope for more “Hall of Fame” examples, but it depends on what I come across over the month. This instalment: poorly designed pie charts.
Pie charts generally are not very useful other than to give a vague idea of relative size. We just aren’t that good at reading angles precisely. Adjacency, colour, the absolute angle, and other factors all confound our ability to read pie charts. Add to that the frequent use of ‘visual bling’ such as 3D perspective which makes it virtually impossible to use the charts for anything other than eye candy. Even if pie charts are useful, the metaphor is that they are pieces of pie. Thus the pieces generally add up to one pie. This point is, unsurprisingly, lost on Fox News. One might expect better from journalists, whose job is ostensibly to inform the public on matters of importance. Even more disappointing is the second chart, from Business Objects, the `business intelligence’ arm of SAP – this is a company that makes visual interfaces as their core business, yet their own pie chart makes no sense at all. Shame!
I don’t claim to even understand the data underlying these charts, but if I had to guess, I’d say perhaps the questions asked about each data item were independent. That is, 70% of people asked “Do you back Palin?” replied “yes”, and 63% replied yes to the same question about Huckabee. In this case, a bar chart would be more appropriate, to understand the relative levels of support. To get data for a pie chart, the question would have to be “Pick one: Palin, Huckabee, Romney”.