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