Pie charts!

HE Festival of Data 2019: Part 3

It’s not often that you get the feeling that you are in a room with a couple of hundred like-minded individuals. This happened at the HE Festival of Data at the University of Huddersfield during a talk by Jackie Njoroge, Director of Strategy at the University of Salford. During Jackie’s talk on the need for timely data to ensure strategic delivery she said in passing that “anyone who presents anything in a pie chart should be …”. This statement met with a round of spontaneous applause, in which I joined, which will course of course come as no surprise to anyone who has heard me lecture on the misuse and misinterpretation of data presentation. My own attitude towards pie charts was crystallised by my PhD supervisor who would always cross out a pie chart in a draft whenever he saw one. Just for fun, and to make the point that they do have valid uses, I included 3 pie charts in my final submitted thesis. This does not detract from the fact that the potential for mis-interpretation with pie charts tends to bring on a rant in a lot of data-oriented people such as myself. Why is this? Well, amongst other things we, people that is, are not very good at judging and comparing angles. Stephen Few has written an excellent piece on pie charts with more detail on this. 

Interestingly we then learned later in the day about another of the issues with pie charts and that is their popularity. People like them, or more specifically, students like them. During their workshop on student dashboards Liz Bennett and Sue Folley from the University of Huddersfield walked us through some work they did with students on the content and presentation of data for student dashboards. Some of this work was published here. One of the findings of their work was how popular pie charts are among students for the presentation of information about them. So we find ourselves in a dilemma. Pie charts are popular but can be mis-interpreted. Should we use them or not? Well, it seems that if the goal is to engage students in their own data then we should use data visualisations they like to look at so pie charts may need to be included. We can always present them electronically which could allow us to add numbers to the charts with, for example, text that appears when you hover over them, reducing some of their drawbacks. It is always important to remember that the goals of data visualisation include not only the need to make it as easy as possible to understand the message in the data but also to engage the viewer in the data. Despite how we may feel about them it looks like pie charts are here to stay. 

The things we have to do to get our message across.

Leave a Reply

Your email address will not be published.