The Plank

Today's Polls: Mccain's Convention Bubble Bursts

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On the strength of an abundance of state and national polling, Barack
Obama has retaken the lead in our Electoral College projection. Our
model now forecasts him to win the election 61.2 percent of the time;
it also gives him a slight, half-point advantage in the popular vote.
Yesterday, Obama was projected to win the Electoral College just 45
percent of the time, so this is a rather dramatic move upward.How can the numbers move so sharply in just 24 hours?
I have tweaked the model slightly at a couple of points recently in
order to make it more sensitive to new information. But these
adjustments are very minor, and their effects are fairly trivial. The
principal reasons these numbers have become more volatile are twofold.
Firstly, we're finally getting into crunch time. The closer we get to
the election, the smaller the true margins of error in the polls, so
relatively small advantages can become more meaningful. But secondly,
we have a lot more data to
look at. If Barack Obama looks like he's moved up a point or two
between two or three polls, that may not be particularly meaningful,
and our model will tend to treat it as noise. If, on the other hand,
Obama appears to have gained a point or two between 20 or 30 polls,
which is what we're getting on a daily basis nowadays, we can say with
more certainty that a real shift in the electorate has occurred.This
is not to say, of course, that every single poll contains good news for
Obama. At least two current national polls (GWU/Battleground and
Economist/YouGov) still have McCain ahead, and a couple more have the
candidates tied. And there are nuggets of good news for McCain in some
of the state polling:Which
of these numbers will McCain partisans like? The +3 from ARG in New
Hampshire. The +7 in Virginia from National Journal. The virtual ties
in Wisconsin, Pennsylvania and Iowa in the Big Ten poll. The +6 in
Florida from SuvreyUSA.And which will Obama partisans like? The
+10 in Colorado from InsiderAdvantage (very probably an outlier, but
outliers are OK when we're able to average them in with other polls).
The +3 in Indiana from Ann Selzer (although remember that Selzer polls
have had a rather strong Democratic lean so far this cycle). Two polls
showing Ohio drawing to a tie, and the same in Florida. The Michigan
number from the Big Ten survey. The Oregon number from the Portland
Tribune. Both of the New Mexico numbers. Maybe the Rasmussen number in
New Jersey.That is, by my count, 10 or 11 or "good" state polls
for Obama and 5 or 6 for McCain. The job of our model is to see the
signal through the noise. There is quite a bit of noise, with so many
pollsters in the field in so many different states, and so many
different factors affecting voter preferences. Eerything from national
news events to advertising blasts in individual states will impact
these numbers -- a really heavy ad buy in a particular state can
sometimes move the numbers there by a couple of points, often only for
no more than 24 hours.But there is also some signal, and today it points toward Obama gaining a tangible amount of ground.*-*A lot of people have asked me to comment on the series of new polling put out by a consortium of Big Ten professors, and by the National Journal,
respectively. Neither of these polls have any track record, and so
there is no completely objective way to evaluate them; our model
assigns any "unknown" pollsters a slightly-below-average rating.
Neither has a statistically significant Democratic or Republican lean,
from what we can tell so far.I like the level of disclosure
provided by the Big Ten polls, which have a complete set of
cross-tabular results available. If you want to gain stature as a "new"
polling outlet, that is the way to do it. The National Journal polls
also provide a fair amount of supporting detail, although it is a bit
more cumbersome to navigate through. Nobody takes politics more
seriously than the boys at the National Journal, so you can assume that
there was a lot of thought given to their methodology. I do wish,
however, that they had elected to go with sample sizes larger than 400
persons, which will produce erratic results even if you're doing
everything else right.

--Nate Silver

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