EXAMPLE 16 Convenience sampling using online polls
Caution: Surveys, like online polls, that use convenience sampling should be treated with a healthy dose of skepticism. They are not statistically sound.
An online newspaper reports that, in an online poll of its readership, 60% say that they get most of their news from online sources. Does this number accurately reflect the proportion of all Americans who get most of their news from online sources?
Solution
No, the sample is not random. Only those Americans who are online already (and already using an online news source) can respond to this online poll. Therefore, the sample is not random, and it is biased. It overestimates the proportion of Americans who get their news from online sources. Further, no mechanism is available to guard against a single person responding repeatedly and getting his or her vote counted multiple times. Online polls are not scientific, and their results should not be considered a true reflection of the sentiments of all Americans.
NOW YOU CAN DO
Exercises 21 and 22.