Pew Research: Landline Polling is Skewing Youth Vote, Favoring McCain

We've been talking about this for at least a year here on Future Majority, but now Pew Research is ready to come out and say it. The number of cell phone-only voters are now numerous enough that their exclusion from traditional polling is skewing the data. A new report from Pew shows that in three straight surveys, lack of cell-only data skewed the survey results 2 - 3% in favor of John McCain.

From the report (emphasis mine):

The Pew Research Center for the People & the Press has conducted three major election surveys with both cell phone and landline samples since the conclusion of the primaries. In each of the surveys, there were only small, and not statistically significant, differences between presidential horserace estimates based on the combined interviews and estimates based on the landline surveys only. Yet a virtually identical pattern is seen across all three surveys: In each case, including cell phone interviews resulted in slightly more support for Obama and slightly less for McCain, a consistent difference of two-to-three points in the margin. [...]

As implied by these results, in each of the three polls, the cell-only respondents were significantly more supportive of Obama (by 10-to-15 percentage points) than respondents in the landline sample. For example, in the September survey Obama led McCain by a 55%-to-36% margin among cell only voters, but the candidates were tied at 45% in the landline sample.

In large part, this reflects the fact that a substantial minority of the cell-only sample is younger than 30 - a demographic group that has consistently backed Obama this year. Traditional landline surveys are typically weighted to compensate for age and other demographic differences, but the process depends on the assumption that the people reached over landlines are similar politically to their cell-only counterparts. These surveys suggest that this assumption is increasingly questionable, particularly among younger people.

As the chart on the right shows, cell-phone only voters under the age of 30 are substantially different in their identification with the Democrats and their support for Obama than are their peers with landline access. Young voters who rely solely on their cell-phones, and thus are often excluded from polls, are far more supportive of Obama and the Democratic Party than are their landline counterparts.

The implications are clear: Obama's youth support, already underrepresented in polls that screen for "likely voters," are further underrepresented due to their phone preferences. As a result, it's not unreasonable to look at the polls that exclude cell-phone samples and compensate for that bias by adding a point to Obama's total and removing a point from McCain's.

For those of us supporting Obama (and biting our nails in recent weeks) that's an encouraging thought, but it also begs a question. This problem isn't going to go away. In fact, it is only going to get worse. As the Pew report points out, cell-phone only voters are growing at a rate of 2% a year, and could be 17% of the electorate in 2008. As that population grows, will pollsters rethink their methodologies to accommodate that shift? And if young voters are being underrepresented due to their cell-phone habits and likely voter screens, what will that mean for the accuracy of the polls leading up to election day? Could the pollsters be as wrong in 2008 as they were in 2004?