Consider the data on the waiting time (seconds) of customers before speaking to a representative at a call center, shown in Exercise 5-9. The data, in sequence, are to be read across the row, before moving to the next row.
(a) Construct an individuals and moving-range chart and comment on the process.
(b) Construct a moving-average chart, with a window of 3, and comment on the process.
(c) Construct an exponentially weighted moving-average chart, with a weighting factor of 0.2, and comment on the process.
(d) Construct a cumulative sum chart, with a target value of 30 seconds, and comment on the process. Assume a type I error level of 0.05.
Exercise
A random sample of 50 observations on the waiting time (in seconds) of customers before speaking to a representative at a call center is as follows:
(a) Construct a histogram and comment on the process.
(b) What assumptions are necessary to test if the mean waiting time is less than 32 seconds?
(c) Make an appropriate transformation to satisfy the assumption stated in part (b) and validate it. Use α = 0.05.
(d) Test to determine if the mean waiting time is less than 32 seconds. Use α =0.05.
(e) Find a 90% confidence interval for the variance of waiting time.