
312 A First Course in Quality Engineering
5.2.4 OC Curve of a P-Chart
The OC curve of a P-chart is made by plotting the p values, proportion defec-
tives in the process, on the x-axis and the probability of acceptance corre-
sponding to the p values on the y-axis� The OC curve of a chart designed for
controlling a process at a particular value—say, p
0
—will give the probabilities
of acceptance by the chart that the proportion defectives produced becomes a
p other than p
0
� The method of calculating the OC is illustrated by Example 5�3�
Example 5.3
Suppose that a process is currently producing 10% defectives—that is, p
0
=
0.10—and