Pie Charts - Great for Hiding Information

Part of the job of product managers (or anyone in business for that matter) is to communicate data.  "How good is this thing?"  Often, people use pie charts to communicate this data in dashboards or presentations. Why do people do this?  

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Part of the job of product managers (or anyone in business for that matter) is to communicate data.  "How good is this thing?"  Often, people use pie charts to communicate this data in dashboards or presentations. Why do people do this?  

As Stephen Few (guru on dashboard design) says:

The truth is, I never recommend the use of pie charts.  ...  Pie charts don't display quantitative data very effectively.  Humans can't compare two-dimensional areas or angles very accurately.

And he's right.  This is an example I pulled from one of our recent internal dashboards.  The problem with this pie chart is that you can't really tell, without reading the numbers the relative size of the pies.  Is the 9.6% slice smaller than the 10.3%?  Is the 22.7% slice double the others or 3x the others?  

You should be able to look at a graph and QUICKLY see the relative comparison without having to read the numbers.  

A better of use of this would be a bar or column chart.  Without the % called out, I can much more quickly see relative size in the bar chart example below.  

Now, I actually disagree with Stephen Few in one respect.  There are cases where you SHOULD use pie charts.  You should use pie charts to hide information.  If you don't want your user to immediately know the differences in values because you want to minimize that particular data point then by all means, use pie charts.  And I'm being honest when there are cases where this can be useful. You may really want your audience to focus and understand one data point, and not pay attention to this other one (if the "other one" is required to be there).  In which case, use a pie chart for the "other one".  This will help make sure they focus on the metric you really want them to be looking at.  Of course, it is best if you can not include the "other one" metric in the first place.  But that isn't always feasible.  

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Now, I actually disagree with Stephen Few in one respect.  There are cases where you SHOULD use pie charts.  You should use pie charts to hide information.  If you don't want your user to immediately know the differences in values because you want to minimize that particular data point then by all means, use pie charts.  And I'm being honest when there are cases where this can be useful. You may really want your audience to focus and understand one data point, and not pay attention to this other one (if the "other one" is required to be there).  In which case, use a pie chart for the "other one".  This will help make sure they focus on the metric you really want them to be looking at.  Of course, it is best if you can not include the "other one" metric in the first place.  But that isn't always feasible.  

I know that the topic of use of "Pie Charts" isn't world changing.  Really, this post is about communication.   The small stuff does matter in communication.  Is showing the value of your product important?  YES!  Get it right.  Spend time on it.