Defective plastic mold. A company that manufactures plastic molded parts believes it is producing an unusually large number of defects. To investigate this suspicion, each shift drew seven random samples of 200 parts, visually inspected each part to determine whether it was defective, and tallied the primary type of defect present. These data are presented in the table below. MOLD Data for Exercise 13.86 Type of Defect Sample Shift # of Defects Crack Burn Dirt Blister Trim 1 1 4 1 1 1 0 1 2 1 6 2 1 0 2 1 3 1 11 1 2 3 3 2 4 1 12 2 2 2 3 3 5 1 5 0 1 0 2 2 6 1 10 1 3 2 2 2 7 1 8 0 3 1 1 3 8 2 16 2 0 8 2 4 9 2 17 3 2 8 2 2 10 2 20 0 3 11 3 3 11 2 28 3 2 17 2 4 12 2 20 0 0 16 4 0 13 2 20 1 1 18 0 0 14 2 17 2 2 13 0 0 15 3 13 3 2 5 1 2 16 3 10 0 3 4 2 1 17 3 11 2 2 3 2 2 18 3 7 0 3 2 2 0 19 3 6 1 2 0 1 2 20 3 8 1 1 2 3 1 21 3 9 1 2 2 2 2

a. From a statistical perspective, are the number of samples and the sample size of 200 adequate for constructing a p-chart for these data? Explain.

b. Construct a p-chart for this manufacturing process.

c. Should the control limits be used to monitor future process output? Explain.

d. Suggest a strategy for identifying the special causes of variation that may be present.