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Two New Reports on Cell Phones and Surveys

Topics: CDC , Cell Phones , NCHS , NHIS , Pew Research Center

The last two days bring news on the issue of cell phones and their impact on political surveys in the form of new reports from the most respected researchers on the subject.

First, yesterday, the Center for Disease Control and Prevention's National Center for Health Statistics released its latest biannual report on the prevalence of households without wireless or standard telephone service (via Bialik). The CDC monitors the cell-phone-only population because it conducts huge ongoing health "surveillance" surveys via telephone, and as such, ask questions about telephone usage on their ongoing, in-person National Health Interview Survey (NHIS). Their latest report, which covers the first six months of the year, shows that 16.1% of adults were reachable only by cell phone, while another 2.1% lacked telephone service of any kind.

081218_NCHSJanuary-June 2008.png

As the chart above shows, the latest survey continues an ongoing, near linear upward growth in the cell-phone-only population. It is worth noting that the hint of a plateau in the trend seen between the second half of 2006 and the first half of 2007 was likely the result of a very slight change in question wording that took effect in 2007. Except for the brief near-pause, the trend has been steadily and consistently upward since 2005.

The second news is the latest report from the Pew Research Center on their efforts to survey voters via cell phone during 2008 (summary, full PDF). It is hard to overstate* the influence of the Pew Center's work on cell phones in the political polling industry. At the PAPOR conference in San Francisco last week, Professor Mike Traugott (a past president of AAPOR and chair of AAPOR's Special Committee on 2008 Primary Polling) noted that earlier this year, "the conventional wisdom in the Spring [among pollsters] was that we didn't have to worry about cell phone only people." At the end of the summer, however, "this conventional wisdom changed drastically" when the Pew Center released its report showing that the omission of cell phone only voters could understate Barack Obama's margin over McCain by two to three percentage points." By the fall, many national media surveys included supplemental cell phone samples in their surveys.

The new Pew report confirms that the patterns they saw, "that estimates based only on landline interviews were likely to have a pro-McCain tilt compared with estimates that included cell phone interviews," persisted through their final survey in late October. It was a difference of a point or two on the margins that "while statistically significant, was small in absolute terms -- smaller than the margin of sampling error in most polls." Of possibly greater importance going forward, they also found similar differences in party identification and self-reported ideology, and bigger differences in (not surprisingly) the use of Internet as a news source and social networking sites like Facebook or MySpace. See the report for the details.

Now that the conventional wisdom on cell-phone only households has shifted among national pollsters, from "it doesn't matter" to "we better account for the them," the Pew Report also points us to the next issue for the c.w. to chew over: Simply interviewing by cell phone (and screening for "cell only" respondents) may not be enough. Pollsters will also need to confront the more difficult issue of how to handle and weight the interviews among what some call "cell phone mostlys:"

Unlike most other polling organizations, Pew's election surveys involved a "full dual frame design," in which people reached by cell phone who also have a landline are interviewed, as well as cell-only respondents. In contrast, most pollsters who included cell phones in their election surveys screened their cell samples for cell-only respondents.

The difference between these two approaches can be seen as a tradeoff in methodological challenges. Supplementing a landline sample with cell-only respondents has the advantage of not "double covering" respondents who have both types of phones. This makes combining the samples more straightforward, but assumes that the landline sample is capable of accurately reaching all adults equally. If some adults have landline phones that they rarely or never answer because they favor their cell phones, they will be underrepresented in these surveys. Pew's approach of interviewing all adults in both the landline and cell phone samples ensures that every adult with a telephone is covered by the survey, but raises challenges in combining the data because some adults had a greater chance to participate if they have more than one telephone. Pew's methodology accounts for this double coverage by weighting respondents with both kinds of phones according to their probability of selection and the regularity with which they use each kind of telephone.

The report goes on to present data showing that the slightly different results produced by the two approaches. Duel users reached by cell phone were more likely to support Obama (53%) than those reached by landline phone (46%). The cell-phone-mostlys reached by cell also identified with the Democrats (54%) more often than those interviewed by landline phone (47%).

The report concludes with a section on the "practical considerations" of interviewing by cell phone. As they have found previously, once they offer a monetary incentive to potential cell-phone respondents ($10), the contact and cooperation rates are comparable to what they get on landline phones. So cell phone interviewing can be done. The downside is that cell-phone interviews cost Pew "nearly two-and-a-half times as much as landline interviews" for reasons they explain in detail.

As always, my summary does little justice to the full report. Go read it all.

*[Mangled use of "understate" corrected]

 

Comments
Vicente Duque:


In the last days Deloitte and the Harrison Group have surveyed the young and old generations and their propensity to be influenced by ads, commercial propaganda in various forms and medias, etc ...

These surveys have found that the Youngest Generations are more influenced by cell phones and their ads and messages ( for consumption ), the Internet and its derivatives and New Tech in general.

Baby Boomers, ages 43 to 61, and the mature generation, ages 62 to 75, are the best TV Viewers and the most influenced by this media.

They also give credibility to Print ads in Magazines and Newspapers.

But they lag in the New Technologies : cell phones, Internet and its new technologies like YouTube, MySpace, Facebook, Twitter, etc ...

Youngsters influence the Media Space by comments on articles, by posting in the mentioned websites, by discussion groups, forums, bloggers, etc ...

The oldest generations are more passive, the youngest are more active, brought up by Barney, the TV Dinosaur : "I love you, You love me".

There is a lot of discussion about Republicans losing these Younger People. McCain projected the image of an Old Man, far removed from the New Technologies.

Raciality.com

Vicente Duque

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