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February 24, 2012

Make measuring change easier with bars instead of pies

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Chart of the Day posted a chart yesterday that directly related to two of my recent post about how to effectively present pie charts:

  1. Pie charts aren't always evil. A confession of a hypocrite.
  2. Tableau Public: Pie Chart Alternatives

In each of these posts I walked through the different options other than pie charts for presenting data across time and compares parts-to-whole relationships.  Here’s the chart from COTD:

It’s pretty easy to see what they are doing here.  Basically they’re comparing market share across operating systems at two times last year.  The biggest problem with this chart is that it’s challenging to compare more than one slice at a time across the pies.  In other words, you can see that Windows share has gone down, but then when you look at Mac’s share, you will probably forget what the Windows change was.

I decided to practice what I preach and put my own recommendations to the test.  Here’s what I came up with:


With my version, I feel it’s much easier to see the market share change because that’s how I’m representing it in the top chart.  The purpose of the COTD blog post was to show the change in market share, so why not present the data as the change in market share? 

I supplemented the chart with a table in the event someone wants to know the exact values.  Notice that I set the values to one decimal place vs. two for COTD.  Two decimals is completely unnecessary precision.

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