Consider the data on the waiting time (seconds) of customers before speaking to a representative at a call center, shown in Exercise 5-8. 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.