Chapter 19, Problem 10E

Inter-State Moving and Storage Company is setting up a control chart to monitor the proportion of residential moves that result in written complaints due to late delivery, lost items, or damaged items. A sample of 50 moves is selected for each of the last 12 months. The number of written complaints in each sample is 8, 7, 4, 8, 2, 7, 11, 6, 7, 6, 8, and 12.

1. a. Design a p-chart and label the mean proportion defective, UCL, and LCL.
2. b. Plot the proportion of written complaints in the last 12 months.
3. c. Interpret the chart. Does it appear that the number of complaints is out of control for any of the months?