EXAMPLE 5 The Plane Truth

According to a USA Today Gallup poll conducted in 2010, 71% of people who had flown at least twice in the past year believed the potential loss of personal privacy from full-body scans or pat-downs was worth it as a method to prevent acts of terrorism. How much do we trust the quality of this survey? Ask first how the sample was selected. On the Gallup website, we learn that the results were based on telephone interviews with a randomly selected national sample of 3018 adults selected using random-digit-dial sampling conducted November 19–21, 2010.

It is a good start toward confidence in the poll to know the intended population, the sample size, the tight window of time (so that there is minimal influence from changes in current events), and—most importantly—random selection. in the next section, we address a few other important considerations.