The controller of a large chemical refinery is concerned about the late processing of some accounts payable, thereby failing to
a. Construct a control chart to analyze this process, using control limits based on the average sample size. Is it appropriate to use the average sample size in this case? Explain. b. Identify the points that should be investigated based on the limits you calculated in part a. How many points did you need to investigate? Is the process in control?
c. Construct another control chart using the max/min approach described in Section 10.4.1.3. How many points do you need to investigate using this approach?
d. Over the next few months the controller challenged the employees to find ways to improve the process. Many suggestions were made and acted upon. Data for the next 30 months are shown below. Has the process improved? Where does it appear that the process has stabilized at a new level of performance? Construct a new control chart for this point onward and estimate the average percentage of payments that are now late.
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