It's not every day that Nate Silver
, a liberal blogger and one of the most respected minds in political statistics, decides that a vast number of polls out there are inaccurate.
The basis for his rejection of so many polls is
simple: they don't call cell phones.
"The percentage of people
who have replaced their landlines with cellphones has climbed at a
remarkably steady rate," begins Silver. When pollsters call only
landlines to ask questions, they wind up excluding cellphone-only households. This oversight has a big effect because "cellphone-only
households ... tend to be younger, poorer, more urban, less white, and
more Internet-savvy. All of these characteristics are correlated with
political viewpoints and voting behavior."
Pollsters try to combat this problem by "weight[ing] their polls by demographics," Silver explains. This weighting is "something
which they need to do anyway, since polls are subject to many forms of
non-response bias (for instance, it's harder to get men on the phone
then women)." But this solution isn't good enough to resolve the cell phone problem, he argues. Pollsters often
don't weight polls "by characteristics like urban/rural location or
martial status, which are predictive of both cellphone usage and
political beliefs," for starters. Silver also points out that
"one may encounter problems when upweighting from very small
subsamples." Pollsters are not going to get very many young adults on the
phone at all--can they extrapolate from the few that they do
manage to get a hold of?
cell phones is quite expensive, acknowledges Silver, but it just might
be necessary to produce accurate polls.
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