In preparation for their 2008 merger, Delta Airlines and Northwest Airlines undertook a comparative study of their on-time performance.
The following table shows each airline€™s on-time record for a common two-month period for three cities where they both operated.

a. Northwest€™s operations executives claim to have superior overall on-time results. Does the data support this claim?
b. Delta€™s executives respond by pointing to its superior performance at key cities. Does the data support this claim?
c. Explain carefully how to reconcile your answers in parts (a) and (b). In your view, which is the better measure of performance€”an aggregate measure or a disaggregatemeasure?

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Delta Airlines Flights Late 484 118 24 626 Northwest Airlines Flights Total Late 120 70 Total New York Chicago Memphis Total 1987 718 193 2898 399 1123 536 2058 412