“Pie charts kill people” vs. “We want pie charts!”

Tobias Komischke / Friday, August 12, 2011

Last month at the Human-Computer Interaction International conference in Orlando, I came across some interesting research results. The be honest, the only reason why I paid attention to those was that the they were authored by a Fraunhofer Institute. Fraunhofer is Europe’s largest application-oriented research organization and the place where I did my first UX-related internship. They also have institutes outside of Europe, and one of those, located in Cambridge, MA,  did a study that compared user preferences of energy management visualizations1

Among other things, twenty subjects completed a forced-choice task on six pairs of contrasting energy data visualizations. For example, they had to make a choice between a column chart and a pie chart visualization of energy costs in private homes. Both visualization types were professionally designed, i.e. 2-dimensional, solid color fill, no crazy glare effects and such.

The results were that 65% of the test persons in the study preferred the visualization that showed the data in a pie chart. 30% preferred the column chart version and 5% couldn’t decide between them.

This outcome is no surprise. In many industries, incl. the financial sector, pie charts are the de-facto standard to show this kind of univariate data. Human factors research has long been showing that column charts (or bar charts, for that matter) are actually faster and more accurate to interpret than pie charts2. So, does this mean we as UX professionals should force column charts upon dashboard users and ignore their preferences and wishes?

I believe a good approach is giving people a choice. At Infragistics, we offer many different data visualization controls to customers who develop dashboards; we cannot and don’t want to dictate which ones to use. Of course, we’re happy to provide guidance. When we in Services execute consulting projects, we design and build UIs that consider human factors. That said, we don’t ignore customer wishes and industry standards. Contrary to popular believe, pie charts actually don’t kill people, they are just not as effective than column charts. So why not giving users a choice? This is what Mint.com is doing: they provide a toggle button that allows the user to switch between a bar chart and a pie chart to show their personal financial data. 

 

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References

1LaMarche, J., Sachs, O. (2011). Designing Interfaces for Home Energy Users:  A Preference Study. In: C. Stephanidis (Ed.): Posters, Part I, HCII 2011, CCIS 173. Springer, Berlin. Pp. 58–62.

2Cleveland, W.S. (1985). The Elements of Graphing Data. Wadsworth, Belmont, CA.