Consider given Exercise, which deals with the average wait time for the arrival of a cab. Using the data in Table 7-25, construct a geometric moving-average control chart. Use a weighting factor of 0.10. What conclusions can you draw from the chart? How is it different from the moving-average control chart constructed in Exercise?
Exercise
The average time (minutes) that a customer has to wait for the arrival of a cab after calling the company has been observed for random samples of size 4. The data for 20 such samples are shown in Table 7-25. Previous analysis gave the upper and lower control limits for an X-chart when the process was in control as 10.5 and 7.7 minutes, respectively. What is your estimate of the standard deviation of the waiting time for a customer? Construct a moving-average control chart using a span of 3. What conclusions can you draw from the chart?
