The main purpose of a data display is to organize and display data to make your point clearly, effectively, and correctly. In this chapter, I present the most common data displays used to summarize categorical and numerical data, thoughts and cautions on their interpretation, and tips for evaluating them.
Pie Charts
A pie chart takes categorical data and shows the percentage of individuals that fall into each category. The sum of all the slices of the pie should be 100% or close to it (with a bit of round-off error). Because a pie chart is a circle, categories can easily be compared and contrasted to one another.
The Florida lottery uses a pie chart to report where your money goes when you purchase a lottery ticket (see Figure 3-1). You can see that half of Florida lottery revenues (50 cents of every dollar spent) goes to prizes, and 38 cents of every dollar goes to education.
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Pie charts and bar graphs for categorical data