A repair shop will send a worker to a caller’s home to repair electronic equipment. Upon receiving a request, it dispatches a worker who is instructed to call in when the job is completed. Historical data indicate that the time from when the server is dispatched until he or she calls is a normal random variable with mean 62 minutes and standard deviation 24 minutes. To keep aware of any changes in this distribution, the repair shop plots a standard exponentially weighted moving-average (EWMA) control chart with each data value being the average of 4 successive times, and with a weighting factor of α = .25. If the present value of the chart is 60 and the following are the next 16 subgroup averages, what can we conclude?

48, 52, 70, 62, 57, 81, 56, 59, 77, 82, 78, 80, 74, 82, 68, 84