Election Polls Landline Biased, Says Pew Research.

By Reporter Wireless and Mobile News on September 26, 2008 10:08 AM

The Pew Research Center for the People & the Press has conducted three major election surveys a vrtually 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. Their analysis concluded that landline polling may be missing out on the young cell-only voters.

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.

Pew concluded that even though the omission of cell phones from election polls does not currently make a large difference in the substantive results, Pew’s surveys this year suggest at least the possibility of a small bias in landline surveys. Such a bias could be consequential in an election that appears to be very competitive right now, especially if significant numbers of young people turn out to vote. In particular, the research suggests that estimates of the candidate preferences of young voters may be biased if cell phone interviewing is not included in the survey.

These problems are all the more pressing as the number of Americans who are reachable only by cell phones increases.

Many polling organizations are including cell phones in their samples this fall, and the Pew Research Center for the People & the Press will include cell phone samples in all of its remaining election polls.

For a broader discussion of the cell phone issue see these earlier Pew Research Center studies:

The Impact of “Cell-Onlys” on Public Opinion Polling
Research Roundup: Latest Findings on Cell Phones and Polling