An ad agency tracks the complaints, by week received, about the billboards in its city:

WEEK 1 2 3 4 5 6 NO. OF COMPLAINTS 4 5 4 11 3 9

a) What type of control chart would you use to monitor this process? Why?

b) What are the 3-sigma control limits for this process? Assume that the historical complaint rate is unknown.

c) Is the process in control, according to the control limits? Why or why not?

d) Assume now that the historical complaint rate has been 4 calls a week. What would the 3-sigma control limits for this process be now? Has the process been in control according to the control limits?