QUESTION 6 (5 marks)

A taxi company wants to do an annual review of its service by checking the number of monthly complaints. The total number of complaints in each of the last 18 months were 15, 9, 13, 12, 9, 20, 8, 10, 16, 11, 18, 3, 10, 12, 5, 22, 32, and 18.

1. If 3-sigma limits are used to construct a control chart (corresponding to 99.73 percent) calculate the upper control limit (UCL) and the lower control limit (LCL) of this control chart. (3 marks)

2. Examining the data and your constructed c chart what can you advise the manager of the taxi company i.e. is the process in control, heading out of control or already out of control? Briefly explain in no more than 1-2 sentences (60 words maximum). (1 mark)

3. The manager of the taxi company has heard of mean and range charts in the statistical quality control field. Explain in no more than 1-2 sentences (60 words maximum) why both a mean and range chart would be unsuitable for this data set. (1 mark)