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Researchers Warn of 'Bias' in Landline-Only Phone Polls Researchers Warn of 'Bias' in Landline-Only Phone Polls

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Researchers Warn of 'Bias' in Landline-Only Phone Polls

Americans continued to abandon their landline telephones in 2012, according to a new report that underscores the importance of sufficient cell-phone interviews for political polls and raises questions about the bias of those surveys that eschew cell phones entirely, like the interactive voice response polls pervading politics today.

More than 38 percent of adults in the U.S. lived in households without a landline telephone during the second half of 2012, the Center for Disease Control and Prevention reported on Tuesday. The vast majority of the 38.2 percent of adults who live in those households have a cell phone, however: 36.5 percent of adults lived in cell-only households, while just 1.9 percent lived in households with no telephone whatsoever.

But most importantly, younger and non-white Americans continue to outpace other groups in replacing landline phones with cell phones. Among adults aged 18-24, 53.2 percent lived in cell-only households, but that number is even higher among Americans aged 25-29 (62.1 percent) and 30-34 (56.7 percent). In comparison, only 11.6 percent of Americans 65 and older are cell-only.

Just over half of Hispanic adults live in cell-only households, the report shows, an increase from the 46.5 percent who were cell-only in the first half of 2012, and nearly twice as many as were cell-only four years ago. In comparison, just 32.9 percent of whites, 39 percent of blacks and 34.4 percent of Asians were cell-only from July-December of 2012. Americans who say they are of mixed race are more likely to be cell-only, the report shows.

The implications for pollsters are clear: Polls that rely too much on landline participation -- or call only landlines -- are going to reach far too many older and whiter voters, and not nearly enough younger or Hispanic voters. "The potential for bias due to undercoverage remains a real threat to surveys conducted only on landline telephones," the CDC report states.

While this problem was just beginning to wreak havoc with survey research and its practices in the latter half of the last decade, the trends from the CDC's reports accentuate the seriousness of the problem.

The increases among middle-aged Americans are particularly troubling for public polling. While only 23.9 percent of those aged 35-44 were cell-only at the end of 2009, that percentage has skyrocketed since. In 2012, a whopping 43.5 percent of Americans aged 35-44 were cell-only, and as those cord-cutting Americans move into their late 40s and 50s, it's expected that landline-substitution percentages among those cohorts will accelerate as well. In 2012, 28.4 percent of Americans aged 45-64 were cell-only, up from 14.9 percent in late 2009.

Pollsters continue to grapple with how to adapt to Americans' changing telephone preferences. In the 1980s, for example, it was possible to reach nearly the entire U.S. adult population by using an automatic, random-digit dialer. Pollsters could then employ certain selection tools -- like asking to speak to the youngest adult male in a household -- to achieve a random sample.

But the popularity of cell phones upended that model. It's illegal for automatic dialers to call cell phones, so those numbers must all be dialed by a human being, which is more costly. Some pollsters have made significant commitments to contacting cell-only Americans, despite the costs. The Gallup Organization conducts half its interviews via cell phone, a change it made in September of last year. For the monthly NBC News/Wall Street Journal poll, 30 percent of interviews are conducted on cell phones.

Campaign pollsters are also grappling with this issue. Democrats came around faster to including cell phones in their samples, but organized efforts from the Republican National Committee and the National Republican Congressional Committee since the 2012 elections have endeavored to set standards for GOP campaign pollsters that peg the minimum cell-phone percentage at 25 percent.

The FCC regulations prohibiting automated dialers from calling cell phones also means that automated polls, like the ones produced by Public Policy Polling on the Democratic side, and the newly-founded Harper Polling on the Republican side, exclude these respondents entirely. Both firms conduct their surveys exclusively on landline phones, meaning, in a national survey, they exclude more than 38 percent of the possible adult universe a priori. (In state polls, this may be even higher. For example, a staggering 51 percent of voters in Arizona last year told exit pollsters that they were cell-only.)

Adjusting polls that don't call a sufficient number of cell phones (or don't call cells at all) is possible, but risky. Cell-only voters made up a third of the 2012 electorate nationally, exit polls show, and they favored President Obama, 54 percent to 43 percent. But among all voters who own a cell phone, Obama won by a slender, 2-point margin. (The reason for that? Mitt Romney actually edged Obama among voters who own both a landline and a cell phone by 2 points.)

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For their parts, both PPP and Harper have expressed interest in finding ways to incorporate cell-only individuals into their polls. Harper Polling co-founder Brock McCleary told Hotline On Call late last year that he could seek to utilize the approach already being used by pollsters like Rasmussen Reports and SurveyUSA -- using the Internet to reach cell-only voters at a lower cost than live interviewers. "I think that the ultimate solution is the combination of an automated process ... and then the online component," McCleary said. (SurveyUSA does conduct some cell-only subsamples via live interviewer, it's worth noting, like the recent poll they conducted for a San Diego TV station in a local congressional race.)

PPP director Tom Jensen was less committal on what his firm would do to incorporate cell phones. "We will likely put out an RFP later this year for folks that would like to work with us in finding a way to give our clients a cost effective way to reach cell phones if that's something they want to pay extra for," Jensen said Tuesday.

Calling the proper number of cell phones is not a guarantee of accuracy: Gallup, which called the most cell phones, was considered among the least accurate survey firms in its 2012 pre-election polls; PPP, which called none, was considered among the most accurate. But as landline substitution continues in a disproportionate manner, it's increasingly likely that landline-only phone polling will be less reliable in the coming years.

DON'T MISS TODAY'S TOP STORIES

Chock full of usable information on today's issues."

Michael, Executive Director

Concise coverage of everything I wish I had hours to read about."

Chuck, Graduate Student

The day's action in one quick read."

Stacy , Director of Communications

Great way to keep up with Washington"

Ray, Professor of Economics

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