Question 12.50

12.50 Purchase order errors.

Purchase orders are checked for two primary mistakes: incorrect charge account number and missing required information. Each day, 10 purchase orders are randomly selected, and the number of mistakes in the sample is recorded. Here are the numbers of mistakes observed for 20 consecutive days (read left to right):

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6 4 11 6 3 7 3 10 14 6
3 5 6 7 5 7 7 4 3 7
  1. What is for the purchase order process? How many mistakes would you expect to see in 50 randomly selected purchase orders?
  2. What are the center line and control limits for a chart for plotting counts of purchase order mistakes per 10 orders? Are there any indications of out-of-control behavior?
  3. Remove any out-of-control observation(s) from the data count series and recompute the chart control limits. Comment on control of the remaining counts.