A branch manager of a brokerage company is concerned with the number of undesirable trades made by her sales staff. A trade is considered undesirable if there is an error on the trade ticket. Trades with errors are canceled and resubmitted. The cost of correcting errors is billed to the brokerage company. The branch manager wants to know whether the proportion of undesirable trades is in a state of statistical control so she can plan the next step in a quality improvement process. Data were collected for a 30-day period and stored in Trade.

a. Construct a control chart for these data.

b. Is the process in control? Explain.

c. Based on the results of (a) and (b), what should the manager do next to improve the process?