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Chapter 18: A. Basic Statistics and Applications 221
Angle of a slice = (Relative frequency of the given category) × 360.
Example 18.19 illustrates the construction of a pie chart using the data in Table
18.5.
Table 18.5 Understanding defect rates as a function of various process steps.
Process steps Frequency Relative frequency Angle size
Initial cutoff 86 86/361 85.75
Turning 182 182/361 181.50
Drilling 83 83/361 82.75
Assembly 10 10/361 10.00
Total 361 1.000 360.00
EXAMPLE 18.19
In a manufacturing operation we are interested in better understanding defect rates as
a function of our various process steps. The inspection points in the process are initial
cutoff, turning, drilling, and assembly. These data are shown in Table 18.5. Construct a
pie chart for the data.
The pie chart for these data is constructed by dividing the circle into four slices.
The angle of each slice is given in the last column of Table 18.5. Thus, the pie chart is as
shown in Figure 18.9. Clearly the pie chart in Figure 18.9 gives us a better understanding
at a glance about the rate of defects occurring at different process steps.
Drilling
23.0%
Assembly
2.8%
Initial cutoff
23.8%
Part IV.A.4
Turning
50.4%
Figure 18.9 Pie chart for defects associated with manufacturing process steps.