2-3 Graphs That Enlighten and Graphs That Deceive 65 FIGURE 2-8 Pareto Chart of Causes of Fatal Plane Crashes YOUR TURN. Do Exercise 11 “Box Office Boffo.” Pie Charts A pie chart is a very common graph that depicts categorical data as slices of a circle, in which the size of each slice is proportional to the frequency count for the category. Although pie charts are very common, they are not as effective as Pareto charts. Feature of a Pie Chart ■ Shows the distribution of categorical data in a commonly used format. Pie Chart of Causes of Fatal Plane Crashes EXAMPLE 5 Figure 2-9a is a pie chart of the same data from Example 4. Construction of a pie chart involves slicing up the circle into the proper proportions that represent relative frequencies. For example, the category of pilot error accounts for 640>1104 or 58% of the total, so the slice representing pilot error should be 58% of the total (with a central angle of 0.58 * 360° = 209°). Figure 2-9b speaks for itself. YOUR TURN. Do Exercise 13 “Box Office Boffo.” FIGURE 2-9a Pie Chart of Causes of Fatal Plane Crashes FIGURE 2-9b Pie Chart That Speaks for Itself One Reason Why Statisticians Are Successful “If you say that there are elephants flying in the sky, people are not going to believe you. But if you say that there are four hundred and twentyfive elephants flying in the sky, people will probably believe you.” —Gabriel García Márquez Cause Frequency Pilot Error 640 Mechanical 195 Sabotage 95 Weather 63 Other 111 TABLE 2-3 Causes of Fatal Plane Crashes
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