By NATE SILVER If you are following some of the same people that I do on Twitter, you may have noticed some pushback about our contention that Barack Obama is a favorite (and certainly not a lock) to be re-elected. I haven’t come across too many analyses suggesting that Mitt Romney is the favorite. (There are exceptions.) But there are plenty of people who say that the race is a “tossup.”
What I find confounding about this is that the argument we’re making is exceedingly simple. Here it is:
Obama’s ahead in Ohio.A somewhat-more-complicated version:
Mr. Obama is leading in the polls of Ohio and other states that would suffice for him to win 270 electoral votes, and by a margin that has historically translated into victory a fairly high percentage of the time.The argument that Mr. Obama isn’t the favorite is the one that requires more finesse. If you take the polls at face value, then the popular vote might be a tossup, but the Electoral College favors Mr. Obama.
So you have to make some case for why the polls shouldn’t be taken at face value.
Some argue that the polls are systematically biased against Republicans. This might qualify as a simple argument had it been true on a consistent basis historically, but it hasn’t been: instead, there have been some years when the polls overestimated how well the Democrat would do, and about as many where the same was true for the Republican. I’m sympathetic to the notion that the polls could be biased, statistically speaking, meaning that they will all miss in the same direction. The FiveThirtyEight forecast explicitly accounts for the possibility that the polls are biased toward Mr. Obama — but it also accounts for the chance that the polls could be systematically biased against him.
Others argue that undecided voters tend to break against the incumbent, in this case Mr. Obama. But this has also not really been true in recent elections. In some states, also, Mr. Obama is at 50 percent of the vote in the polling average, or close to it, meaning that he wouldn’t need very many undecided voters to win.
A third argument is that Mr. Romney has the momentum in the polls: whether or not he would win an election today, the argument goes, he is on a favorable trajectory that will allow him to win on Tuesday.
This may be the worst of the arguments, in my view. It is contradicted by the evidence, simply put.
In the table below, I’ve listed the polling averages in the most competitive states, and in the national polls, across several different periods.
First are all polls from June 1, the approximate start of the general-election campaign, until the start of the party conventions.
Next are the polls between the conventions and the first debate in Denver in early October.
Finally are the polls since that first debate in Denver. It’s been roughly 30 days since then. If Mr. Romney has the momentum in the polls, then this should imply that his polls are continuing to get better: that they were a little better this week than last week, and a bit better last week than the week before. So these polls are further broken down into three different periods of about 10 days each, based on when the poll was conducted.
What type of polling average is this, by the way? About the simplest possible one: I’ve just averaged together all the polls of likely voters in the FiveThirtyEight database, applying no other weighting or “secret sauce.”
If you evaluate the polls in this way, there is not much evidence of “momentum” toward Mr. Romney. Instead, the case that the polls have moved slightly toward Mr. Obama is stronger.
In 9 of the 11 battleground states, Mr. Obama’s polls have been better over the past 10 days than they were immediately after the Denver debate. The same is true for the national polls, whether or not tracking polls (which otherwise dominate the average) are included. FULL POST