Question: Referring to Problem, assume the Ajax managers determine any issues identified by the control charts were caused by one time events. The data for weeks 41 through 45 are in the Ajax-Extra file.
a. Using the control limits developed from the first 40 weeks, do these data indicate that the process is now out of control? Explain.
b. If a change has occurred, brainstorm some of the possible reasons.
c. What will be the impact on the control charts when the new data are included?
d. Use the data in the files Ajax and Ajax-Extra to develop the new control charts.
e. Are any of the typical control chart signals present? Discuss.
Problem: The Ajax Taxi company in Manhattan, New York, wishes to set up an x-chart and an R-chart to monitor the number of miles driven per day by its taxi drivers. Each week, the scheduler selects four taxis and (without the drivers' knowledge) monitors the number of miles driven. He has done this for the past 40 weeks. The data are in the file Ajax.
a. Construct the R-chart for these 40 subgroups.
b. Construct the x-chart for these 40 subgroups. Be sure to label the chart correctly.
c. Look at both control charts and determine if any of the control chart signals are present to indicate that the process is not in control. Explain the implications of what you have found for the Ajax Taxi Company.