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WASHINGTON -- Watching the polls to figure out who's up and who's down this election season? Be careful. The poll may have a pro-Republican bias.
The ranks of Americans who use only cell phones have skyrocketed. Some public polls don't survey them, however, and they miss a group of people who are more likely to vote Democratic, including the young, the poor, Hispanics and African-Americans.
The nonpartisan Pew Research Center recently found that in four out of five national polls this year, polls that contact only those with land-line phones gave Republicans a 4- to 6-percentage-point edge over Democrats, compared with polls that included cell phones.
In the most recent poll, a survey of likely voters reached via land lines gave Republicans a 12-point edge, 53-41 percent. Polls that also called voters who only use cell phones found the Republican edge was 7 points, 50-43 percent.
"Cell-only adults are demographically and politically different than those who live in land-line households," the Pew report said. "As a result, election polls that rely only on land-line samples may be biased."
The challenge in measuring public opinion has grown as more Americans rely on cell phones. In four and half years, the percentage of Americans 18 and older who rely only on cell phones has skyrocketed from 9.6 percent to 22.9 percent, according to the National Center for Health Statistics.
Similarly, the tally of households with cell phones only has risen from 10.5 percent to 24.5 percent. Another 14.9 percent of homes have land lines but report receiving most or all calls via cell phones.
Who are these cell-phone-only people? According to the National Center for Health Statistics:
-The young: 49 percent of those aged 25-29, and 38 percent of those aged 18-24.
-The less-educated: 25 percent of those with high school educations or less, the most wireless group.
-Students: 29 percent of people who go to school.
-Hispanics: 30 percent, the most wireless of any race or ethnicity, with African-Americans at 25 percent and non-Hispanic whites at 21 percent.
-The poor: 36 percent.
-Renters: 43 percent.
Many public polls this election season do include calls to cell phone-only voters, including McClatchy-Marist polls. But some don't, including automated surveys, such as the Rasmussen poll, that use computer-generated dialing and interviews.
"All things being equal, cell phones need to be included," said Lee Miringoff, the director of the Marist Institute for Public Opinion at Marist College, which conducts the McClatchy-Marist poll.
"You don't want to systematically exclude a group that may have different attitudes. It's a large enough group that you can't assume that they mirror the rest of the population."
Calls to Rasmussen for comment weren't returned.
Calling cell phones for a poll is more challenging and expensive than calling land lines.
First, Miringoff said, Federal Election Commission regulations require that they be dialed manually. Second, a questioner has to ask whether the person is driving or using heavy equipment. A "yes" answer requires a follow-up call later. Third, a high percentage of people with cell phones are younger than 18 and unable to vote. Fourth, many people refuse to answer the calls because they must pay for the air time; often pollsters compensate them, further driving up costs.
Overall, the "yield" of usable results from cell phone calls is about one-third of the calls to land-line phones, Miringoff said. He cautioned, however, that the pro-Republican bias can be slight or overstated.
In Wisconsin, for example, Democratic Sen. Russ Feingold's campaign last week disputed the McClatchy-Marist poll and others that found Feingold trailing his Republican opponent. One complaint: Polls were missing cell phone users and thus likely Feingold supporters.
But Marist included cell phones in its sample. While Feingold trailed Republican Ron Johnson by 46-51 percent among land-line phone users, he trailed by a larger margin, 40-56 percent, among cell phone users.
"The cell phone users are not helping him at all. In fact, he's trailing among them," Miringoff said. "The problem for Feingold is not in the polling; it's in the voter preferences. We're seeing similar things in Colorado as well. The whole enthusiasm thing is more salient than the mode of communication."
ON THE WEB:
-Pew Research Center report on cell phones and polls: http://pewresearch.org/pubs/1761/cell-phones-and-election-polls-2010-midterm-elections