In 1997, the response rate to a typical telephone poll was a healthy 36 percent, according to Pew. By 2012, it had fallen to 9 percent. Fortunately, many surveys appear to be doing a good job of weighting the answers of people who do respond, to make up for those who don’t. Still, the long-term reasons for concern are clear: People who are more likely to avoid polls, such as anyone born after, say, 1980, are different from those who answer them.
The response rate of the Labor Department’s monthly jobs survey is far higher (about 89 percent) than that of a political poll, but it has also fallen (from 96 percent in the 1980s). Not surprisingly, the people who do not respond have different experiences in the job market than those who do.
That is from David Leonhardt. One implication is that actual unemployment may be higher than we are measuring.