The classic application of confidence intervals is political polling: the science of sampling relatively few people to predict the opinions of a large population. However, in the 2010s, the art of political polling — constructing representative samples from a large population — has become more and more difficult. FiveThirtyEight.com had a nice feature about problems that pollsters face today that were not issues a generation ago. A sampling:
The problem is simple but daunting. The foundation of opinion research has historically been the ability to draw a random sample of the population. That’s become much harder to do, at least in the United States. Response rates to telephone surveys have been declining for years and are often in the single digits, even for the highest-quality polls. The relatively few people who respond to polls may not be representative of the majority who don’t. Last week, the Federal Communications Commission proposed new guidelines that could make telephone polling even harder by enabling phone companies to block calls placed by automated dialers, a tool used in almost all surveys.
What about Internet-based surveys? They’ll almost certainly be a big part of polling’s future. But there’s not a lot of agreement on the best practices for online surveys. It’s fundamentally challenging to “ping” a random voter on the Internet in the same way that you might by giving her an unsolicited call on her phone. Many pollsters that do Internet surveys eschew the concept of the random sample, instead recruiting panels that they claim are representative of the population.