Then there’s the difficulty in getting potential voters to agree to be interviewed by phone (polls used to be conducted face-to-face), especially since many people now use cell phones only. Federal law requires cell phones to be hand-dialed rather than dialed by computers as land lines are.
“In addition, it's getting much harder for pollsters to get people to respond to interviews,” Mr. Barone writes. “The Pew Research Center reports that it's getting only 9 percent of the people it contacts to respond to its questions. That's compared with 36 percent in 1997.”
“Are those 9 percent representative of the larger population?” Barone asks. “As that percentage declines, it seems increasingly possible that the sample is unrepresentative of the much larger voting public. One thing a poll can't tell us is the opinion of people who refuse to be polled.”
The conservative complaint is that Democrats are being over-sampled in polls. Pollsters say their random sampling of voters surveyed just reflects the way people identify themselves politically (which is not necessarily the same as how they're registered) – 35 percent Democrats, 28 percent Republicans, and 33 percent Independents.
“The polls have no such history of partisan bias, at least not on a consistent basis,” he wrote Saturday. “There have been years, like 1980 and 1994, when the polls did underestimate the standing of Republicans. But there have been others, like 2000 and 2006, when they underestimated the standing of Democrats.”