THE MISUNDERSTOOD AND MALIGNED PIE CHART
The pie chart is undoubtedly the graphical illustration with the worst reputation. Wilkinson (1999) points out that the pie chart is simply a bar chart that has been converted to polar coordinates. Therein lies the problem: most humans naturally think in Cartesian coordinates.
Focusing on Wilkinson’s point makes it easier to understand that the conversion of the bar height to an angle on the pie chart is most effective when the bar height represents a proportion. If the bars do not have values where the sum of all bars is meaningful, the pie chart is a poor choice for presenting the information (c.f. Figure 10.13).
Rule 7: Do not use pie charts unless the sum of the entries is scientifically meaningful and of interest to the reader.
On the other hand, the pie chart is an effective display for illustrating proportions. This is especially true when we want to focus on a particular slice of the graphic that is near 25% or 50% of the data, since we humans are adept at judging ...
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