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230 Part IV: Quality Assurance
Continued
b. Having completed the frequency distribution table, we are ready to construct the
histograms. To construct the frequency histogram we first mark the classes on the x-axis
and the frequencies on the y-axis. Remember that when we mark the classes on the
x-axis we must make sure there is no gap between the classes. Then on each class
marked on the x-axis, place a rectangle so that the height of each rectangle is proportional
to the frequency of the corresponding class. The frequency histogram for the
data with a frequency distribution as given in Table 18.9 is shown in Figure 18.15.
To construct the relative frequency histogram, just change the scale on the y-axis
in Figure 18.15 so that instead of plotting the frequencies, we can plot relative frequencies.
The resulting graph shown in Figure 18.16 is the relative frequency histogram for
the data with the relative frequency distribution given in Table 18.9.
10
Frequency
5
0
30 54 78 102 126 150 174 198
Data
Part IV.A.4
Figure 18.15
Frequency histogram for survival time of parts under extreme operating
conditions.
10/50
Relative frequency
5/50
0.0
30 54 78 102 126 150 174 198
Data
Figure 18.16
Relative frequency histogram for survival time of parts under extreme
operating conditions.