October 31, 2012, 10:38 am535 CommentsOct. 30: What State Polls Suggest About the National Popular Vote By NATE SILVERMitt
Romney and President Obama remain roughly tied in national polls, while
state polls are suggestive of a lead for Mr. Obama in the Electoral
College. Most people take this to mean that there is a fairly good
chance of a split outcome between the Electoral College and the popular
vote, as we had in 2000. But the story may not be so simple
For
both the swing state polls and the national polls to be right,
something else has to give to make the math work. If Mr. Obama is
performing well in swing states, but is only tied in the popular vote
nationally, that means he must be underperforming in noncompetitive
states.But polls of noncompetitive states don’t always cooperate with the story. Take the polls that were out on Tuesday.

Mr. Obama trailed by “only” eight points, for instance, in a poll
of Georgia that was released on Tuesday. Those are somewhat worse
results than Mr. Obama achieved in 2008, when he lost Georgia by five
percentage points. But they’re only a little bit worse, whereas the
national polls are suggestive of a larger decline for Mr. Obama in the
popular vote.Or take the poll
of Texas, also out on Tuesday, which had Mr. Obama behind by 16 points
there. He’s obviously no threat to win the state or come close to it,
but that still represents only a 4-point decline for Mr. Obama from
2008, when he lost Texas by 12 points instead.High-population red states like these, Texas and Georgia, are just the sort of places where Mr. Obama would need to lose a lot of ground in order to increase the likelihood of his winning the Electoral College while losing the popular vote.

Perhaps
Mr. Obama is underperforming in deeply blue states rather than deeply
red ones? Sometimes you’ll get numbers that check out with this
assumption: Mr. Obama did get some mediocre polling in Oregon on
Tuesday, for instance. But he also got a poll showing him ahead by 23
points in California. Another survey on Tuesday gave him a 31-point lead
in Massachusetts.Yes, I am deliberately cherry-picking a bit.
But the discrepancy seems to hold if you look at the data in a more
comprehensive way. Nor is it an unusual feature of the FiveThirtyEight
model. Rather, pretty much every method for evaluating the election
based on state polls seems to hint at a very slight popular vote lead
for Mr. Obama, along with an Electoral College one.In the table
below, I’ve listed the current forecasts at seven different Web sites
that use state polls, sometimes along with a modicum of other
information like a state’s past voting history, to produce predictions
of the popular vote in each state.The first of these sites is FiveThirtyEight. The others, in the order that they’re listed in the table, are Electoral-Vote.com; Votamatic, by the Emory University political scientist Drew Linzer; HuffPost Pollster; Real Clear Politics; Talking Points Memo’s PollTracker; and the Princeton Election Consortium,
which is run by Sam Wang, a neuroscientist at Princeton. These are
pretty much all the sites I’m aware of that use state polling data in a
systematic way.
You
can see that the various projections strongly agree with another, for
the most part, in making “calls” about individual states. The only state
where different sites show different candidates ahead right now is
Florida, where Talking Points Memo gives Mr. Obama a nominal
0.2-percentage point lead while the others (including FiveThirtyEight)
have Mr. Romney slightly up instead. There are also four states — New
Hampshire, Iowa, Colorado and Virginia — in which some methods show an
exactly tied race while others give Mr. Obama the lead.Although I
hope that this chart serves as a useful reference point — and as a
reminder that other data-driven sites that look at the polls with the
same philosophy that FiveThirtyEight applies are achieving largely the same results — I’m more interested in looking at this data in a macroscopic way.Suppose,
for example, that you take the consensus forecast in each state. (By
“consensus” I just mean: the average of the different forecasts.) Then
you weigh it based on what each state’s share of the overall turnout was
in 2008, in order to produce an estimate of the national popular vote.Do
the math, and you’ll find that this implies that Mr. Obama leads
nationally by 1.9 percentage points — by no means a safe advantage, but
still a better result for him than what the national polls suggest.What
if turnout doesn’t look like it did in 2008? Instead, what if the share
of the votes that each state contributed was the same as in 2004, a
better Republican year?That doesn’t help to break the discord
between state and national polls, unfortunately. Mr. Obama would lead by
two percentage points in the consensus forecast weighing the states by
their 2004 turnout.Or we can weigh the states by their turnout in
2010, a very good Republican year. But that doesn’t help, either:
instead, Mr. Obama leads by 2.1 percentage points based on this method.(In
each of these examples, you’d get almost exactly the same outcome if
you used the FiveThirtyEight forecast alone rather than the consensus.
We’re on the high end and the low end of the consensus in different
states for Mr. Romney and Mr. Obama, but it pretty much balances out
over all.)Whether the state polls or the national polls characterize the election correctly could well determine its outcome.

Mr.
Obama’s lead in the Electoral College is modest, but also quite
consistent across the different methods. The states in which every
site has Mr. Obama leading make up 271 electoral votes — one more than
the president needs to clinch victory. The states in which everyone has
Mr. Romney ahead represent 206 electoral votes. That leaves five states,
and 61 electoral votes, unaccounted for — but Mr. Obama would not need
them if he prevails in the states where he is leading in the polls.But
perhaps national polls tell the right story of the race instead —
meaning that the state polls systematically overrate Mr. Obama’s
standing?It’s certainly possible. (It keeps me up late at night.)
If the polls in states like Ohio and Wisconsin are wrong, then
FiveThirtyEight — and all of our competitors that build projections
based on state polls — will not have a happy Nov. 6.With that
said, our decision to cast our lot mostly with the state polls is not
arbitrary. In recent years, they’ve been a slightly more unbiased
indicator of how the election will play out.Bias, in a statistical sense, means missing consistently in one
direction — for example, overrating the Republican’s performance across
a number of different examples, or the Democrat’s. It is to be
distinguished from the term accuracy, which refers to how close you come to the outcome in either
direction. If our forecasts miss high on Mr. Obama’s vote share by 10
percentage points in Nevada, but miss low on it by 10 percentage points
in Iowa, our forecasts won’t have been very accurate, but they also won’t have been biased since the misses were in opposite directions (they’ll just have been bad).In a previous article,
I examined the history of bias in public polls based on whether they’ve
tended systematically to overrate the standing of the Democrat or the
Republican. (The answer is that they don’t exhibit either bias on a
consistent basis, as long as you’re using likely voter polls; registered
voter polls will tend to overstate the vote for the Democrat.)This
article also contained a comparison between state and national polls in
the presidential race: which have been more free of bias?
In
recent elections — since state polling data became more robust — it’s
the state polls that have done a bit better. This was especially so in
1996, when national polls implied a double-digit victory for Bill
Clinton over Bob Dole (and Ross Perot) but state polls were more in line
with the single-digit victory that he actually achieved. In 2000, state
polls provided an accurate portrayal of a too-close-to-call race, while
national polls missed high on George W. Bush vs. Al Gore.There
have been other years like 1992 in which the national polls did a bit
better. But on average since that year, the state polls have had a bias
of 1.1 percentage points — half as much as the national polls, which
have had a 2.1-point bias instead.We’re approaching the point
where Mr. Romney may need the state polls to be systematically biased
against him in order to win the Electoral College. And that certainly
could turn out to be the case: if Mr. Romney wins the popular vote by
more than about two percentage points, for example, he’ll be very likely
to cobble together a winning electoral map, somehow and some way. (And
he’ll be a virtual lock if the results are in line with Mr. Romney’s
best national polls, like the Gallup survey, which put him four or five
points ahead.)But the historical evidence weighs in slightly more
heavily on behalf of the state polls, in my view, when they seem to
contradict the national ones. If the state polls are right, than Mr.
Obama is not just the favorite in the Electoral College but probably
also in the popular vote.Tuesday’s Polls

Mr.
Obama made gains in the FiveThirtyEight forecast on Tuesday, with his
chances of winning the Electoral College increasing to 77.4 percent.A
fair amount of this boils down to Ohio, where three polls released on
Tuesday gave Mr. Obama leads by margins ranging from three to five
percentage points. Two of the polls, from Grove Research and the Mellman
Group, generally show strong results for Democrats, which give them
less impact in the forecast after applying our adjustment for pollster “house effects”.
Still, the three polls taken collectively were enough to widen Mr.
Obama’s projected lead in Ohio to 2.4 percentage points from 2.1 on
Monday. Given how central Ohio is
to each candidate’s electoral strategy — and how little time remains in
the race — this was enough to improve Mr. Obama’s Electoral College
chances. (The forecast does not yet account for the poll
by Quinnipiac University for The New York Times and CBS News, which had
Mr. Obama five points ahead in Ohio but which was released after we had
run the model for the night.)
Another poll
that received a lot of attention on Tuesday was one by Glangariff Group
Inc. in Michigan, for The Detroit News. That survey had Mr. Obama ahead
by only 2.7 points in Michigan.There has been some odd polling in Michigan this year,
but the Detroit News polls have not been a big part of the problem.
Instead, its surveys have usually come pretty close to the polling
consensus in the state. Furthermore, this survey suggests tightening in
the race in Michigan since earlier this month, when a poll by the same
firm had Mr. Obama ahead by 6.7 percentage points instead.Nonetheless,
Michigan is probably not as close as two or three points right now:
most polls released after the first debate in Denver suggested a lead
for Mr. Obama in the mid-to-high single digits. Usually, states do not
shift all that much relative to others in their region. The fact that
Mr. Obama’s polling has held up reasonably well in Ohio and Iowa, for
example, is reason to suspect that some of the movement in the poll
represents statistical noise, even if it comes from a good polling
company.Perhaps more important, we’re at the stage in the race where getting a relatively
good poll does not matter all that much: the question is which
candidate is ahead outright in enough states to secure 270 electoral
votes. Michigan deserves to be monitored over the final week of the
campaign, but in all probability Mr. Romney’s more likely paths to
victory will run through Ohio instead.Mr. Obama had a somewhat
above-average day in national polls on Tuesday, which had him up in the
race by about one percentage point on average. Part of this is because
the Gallup poll, which has shown very poor results for Mr. Obama, did
not publish results on account of Hurricane Sandy.
Perhaps the most intriguing result from this group is the poll
from Google Consumer Surveys. (Yes, Google has begin to conduct surveys
online.) That poll had Mr. Obama ahead by four percentage points, an
improvement from a roughly 1-point deficit for Mr. Obama in their prior
survey last week.The Google survey could be an
indication that the effects of the hurricane will play somewhat to Mr.
Obama’s political advantage. But it will probably be Thursday or Friday,
once power and some of the national tracking surveys that have been
discontinued have come back online, before we can say so with much
confidence.In the meantime, the state polls continue to hint that
Mr. Obama remains the favorite to win the Electoral College — and if
the state polls are right, he may well be the favorite in the popular
vote as well.


ABOUT NATE SILVER:

Nathaniel Read "Nate" Silver (born January 13, 1978) is
an American statistician, sabermetrician, psephologist, and writer. Silver first gained public recognition for
developing PECOTA,[2] a system for
forecasting the performance and career development of Major League
Baseball players, which he sold to and then managed for Baseball
Prospectus from 2003 to 2009.[3]
In 2007, writing under the pseudonym "Poblano", Silver began to publish
analyses and predictions related to the 2008 United States
presidential election. At first this work appeared on the political blog Daily Kos, but in March 2008 Silver
established his own website, FiveThirtyEight.com. By summer of that
year, after he revealed his identity to his readers, he began to appear as an
electoral and political analyst in national print, online, and cable
news media.
The accuracy of his November 2008 presidential election predictions—he
correctly predicted the winner of 49 of the 50 states—won Silver further
attention and commendation. The only state he missed was Indiana, which went for
Barack Obama by 1%. He
also correctly predicted the winner of all 35 Senate races that year.
In April 2009, he was named one of The World's 100 Most Influential People by Time.[4]


In 2010, Silver's FiveThirtyEight blog was licensed for publication by
The New York
Times.[5][6] The newly renamed
blog, FiveThirtyEight: Nate Silver's Political Calculus,[7] first appeared in
The Times on August 25, 2010. In 2012, FiveThirtyEight won a Webby
Award as the "Best Political Blog" from the International Academy of Digital
Arts and Sciences.
Silver's book The Signal and the Noise was published in September
2012.


http://fivethirtyeight.blogs.nytimes.com/