Nov. 5: Late Poll Gains for Obama Leave Romney With Longer Odds
By NATE SILVER
Mitt Romney has always had difficulty drawing a winning Electoral College hand. Even during his best period of polling, in the week or two after the first presidential debate in Denver, he never quite pulled ahead in the polling averages in Ohio and other states that would allow him to secure 270 electoral votes.
But the most recent set of polls suggest another problem for Mr. Romney, whose momentum in the polls stalled out in mid-October. Instead, it is President Obama who is making gains.
Among 12 national polls published on Monday, Mr. Obama led by an average of 1.6 percentage points. Perhaps more important is the trend in the surveys. On average, Mr. Obama gained 1.5 percentage points from the prior edition of the same polls, improving his standing in nine of the surveys while losing ground in just one.
Because these surveys had large sample sizes, the trend is both statistically and practically meaningful. Whether because of Hurricane Sandy, the relatively good economic news of late, or other factors, Mr. Obama appears to have gained ground in the closing days of the race.
The national polls now range from showing a 1-point lead for Mr. Romney to slightly more than a 4-point advantage for Mr. Obama. The FiveThirtyEight forecast of the national popular vote is within this range, projecting Mr. Obama’s most likely margin of victory to be two or three percentage points, approximating the margin that George W. Bush achieved in defeating John Kerry in 2004.
Averaging polls together increases their sample size — making them much more powerful statistically than any one poll taken alone. But the errors in the polls are sometimes correlated, meaning there are years when most of them miss in the same direction. Mr. Romney remains close enough to Mr. Obama that he could fairly easily win the popular vote if there is such an error in Mr. Obama’s favor this year.
Mr. Romney’s chances are less, however, of winning the Electoral College. The large majority of polls in battleground states over the past three days have shown leads for Mr. Obama. On Monday, for example, 19 battleground state polls found leads for Mr. Obama, as compared with just three for Mr. Romney.