Imagine an airline hires us to consult as to why its customers are unhappy according to survey data. We have strong reason to doubt that our client, the airline, attracts especially grumpy passengers. After applying the statistical lessons we learned earlier in this book, we note the complaints about bad flight crew service are coming from a particular cross section of airports. We notice the same aircrews and airplanes cycle through other airports, with few passenger satisfaction problems. The problems are with these airports in particular. How could this be?