To construct a p-chart for a manufacturing process, 25 samples of size 200 were drawn from the process. The number of defectives in each sample is listed below.
a. Calculate the proportion defective in each sample.
and
b. Calculate the plot p-bar and the upper and lower control limits for the p-chart.
and
c. Calculate and plot the A, B, and C zone boundaries on the p-chart.
and
d. Plot the sample proportions on the p-chart and connect them with straight lines.
and
e. Use the pattern-analysis rules 1-4 for detecting the presence of special causes of variation (Figure 12.21) to determine whether the process is out of control.
Sample Sample Size Defectives
1 120 11
2 120 5
3 120 4
4 120 8
5 120 10
6 120 13
7 120 9
8 120 8
9 120 10
10 120 11