An airline records quarterly customer complaints in the last year as follows Qua

Question

An airline records quarterly customer complaints in the last year as follows Quarter OI 02 Q3 OA4 No. of Complaints 152 103 130 287 You are asked to construct a 2-sigma statistical control chart to check if the airline needs to pay extra attention to certain quarters to improve customer satisfaction and lower the number of complaints in the next year Based on the control chart, how many quarters in the last year are considered as NOT in control require extra attention)? Is the whole process in control? Select one: a. four quarters; NOT in control b. three quarters; NOT in control c.O quarter, in control d. one quarter; NOT in control e. two quarters; NOT in control

Explanation / Answer

We can construct a C chart for same

Cbar = average number of complaints = ( 152 +103 + 130 + 287 ) / 4 = 168

Thus Upper control Limit basis 2 sigma statistical control :

UCL = Cbar + 2 x square root ( Cbar ) = 168 + 2 x Square root ( 168 ) = 168 + 2 x 12.96 = 168 + 25.92 = 193.92

The lower control limit basis 2 sigma statistical control :

LCL = Cbar - 2 x square root ( Cbar ) = 168 – 2 x square root ( 168 ) = 168 – 2 x 12.96 = 168 – 25.92 = 142.08

Therefore control limit range is 142.08 – 193.92 . The process will be considered to be in control if all the values of number of complaints are within above control limit range.

However , data for Q2, Q3 and Q4 are outside above control limit range . Therefore, process is out of control .

ANSWER : b ) THREE QUARTERS , NOT IN CONTROL

ANSWER : b ) THREE QUARTERS , NOT IN CONTROL

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