CheersInc., a small health insurance company, manages its own call center to provide customer service. A call is first taken by a general representative who will try to resolve the client's inquiry. If the general representative cannot assist the client, he will forward the call to the respective specialized unit. As part of its quality control system, management decided that call durations at the general representative level should be between 5 and 7 minutes.

The tables below show the results of five samples taken at different hours along with the corresponding control limits using the sample data:

The call center supervisor is concerned because the range in Sample 5 is outside the control limits and wants to determine the source of that deviation. Her manager appreciated her concern but told her she was overreacting "because, since all the data points are within 4 and 7 minutes, how can it possibly be out of control?"

In the scenario about CheersInc. above, if the call center wants its process at the general representative level to be six-sigma capable, how much should the process standard deviation be in minutes? You can use your tools from the course to find your answer.

To be z-sigma capable the Cp has to be equal to 1. Using the USL and LSL given above ( 7 and 5 minutes) and z=6, determine the value of the standard deviation (sigma) that makes the Cp=1.