Evaluation and data visualization folks may disagree on the best pie to serve at Thanksgiving dinner. Pumpkin? Pecan? A nice silk pie made with chocolate liqueur and tofu? (Thank you, Alton Brown.)
You see, the whole point of charts is to give people an instantaneous understanding of your findings. Your readers can easily discern differences in bars and lines. In wedges of pie, not so much. Data visualization expert Stephen Few explained the problem during this interview with the New York Times: “When looking at parts of a whole, the primary task is to rank them to see the relative performance of the parts. That can’t be done easily when relying on angles formed by a slice.”
(Note: This parts-to-whole angle problem may also explain why most of us can’t understand how our Whole Foods pumpkin pie could possibly have eight servings. Eight? Are you kidding me?)
So, for today’s pre-Thanksgiving holiday post, I thought I would point you to some online articles about the much used and much vilified pie chart.
First, here’s an article by American Evaluation Association’s president-elect John Gargani, arguing for retirement of the venerable pie chart. He make points that are repeated in many anti-pie chart blog posts. But in the interest of objectivity, you should know that agreement to send pie charts to the cosmic dust bin is not universal. Here’s a post by Bruce Gabrielle of Speaking PowerPoint that describes situations where pie charts can shine.
In general, most experts believe that the times and places to use pie charts are few and far between. If you have found one of those rare times, then here’s a post at Better Evaluation with the design tips to follow.
But for heaven sake, turn off that three-dimensional feature in your pie chart, or in any chart, for that matter. Nobody wants to see that!
And for humorous examples of what not to do, check out Michael Friendly’s Evil Pies blog,