These data compare the on-time arrival performance of United and US Airways. The table shows the status of 13,511 arrivals during January 2006.

(a) On the basis of this initial summary, find the percentages (row or column) that are appropriate for comparing the on-time arrival rates of the two airlines. Which arrives on time more often?
(b) The next two tables organize these same fights by destination. The first also shows arrival time and the second shows airline. Does it appear that a lurking variable might be at work here? How can you tell?

(c) Each cell of the following table shows the number of on-time arrivals for each airline at each destination. Is Destination a lurking factor behind the original 2 × 2 table?

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Status On time Delayed United 6,291 1,466 US Airways 4,366 1,388 Status Dallas Denver Minneapolis Philadelphia On time 829 5,661 Delayed 205,205160 518 3,649 1,284 Airline Dallas Denver Minneapolis Philadelphia United 450 6,323 US Airwavs 474 510 584 543 204 4,423 Airline Dallas Denver Minneapolis Philadelphia United 359 5,208 US Airwavs 360 364 470 453 158 3,285