I apologize to all for the late update. We wanted to make sure all the polls were in. And it’s a hectic day.
The following are final estimates, based on taking polling data over longer intervals than our usual 1-week rule. Instead, I found the period over which a state’s polling variance was minimized, as a means of identifying stability.
ELECTORAL PREDICTION (mode): Barack Obama 303 EV, Mitt Romney 235 EV. The mode is the single most frequent value on the EV histogram. It corresponds to the map below, and has a 22% chance of being exactly correct. The next-most-likely outcome is Obama 332, Romney 206 EV.
ELECTORAL PREDICTION (median): Obama 305 EV, Romney 233 EV, Popular Vote Meta-Margin Obama +2.76%. This median is almost guaranteed to be off, since 305 EV is not a common combination. It is the midpoint of all possibilities, and reflects the overall shape of the distribution. The nominal 1-sigma band is Obama [293, 332] EV.
TWO-CANDIDATE POPULAR VOTE SHARE: Obama 51.1%, Romney 48.9%.
As I wrote late last night, Florida is a hard case. Several new polls came out this morning, making the median basically zero. As a tie-breaker I resorted to mean-based statistics. I will be unsurprised for it to go either way. Nate Silver and Drew Linzer went the other way. We are all tossing coins. I am prepared to lose the coin toss.
In Florida, a recount is triggered by a margin of 0.5% or less (recount rules, Brennan Center for Justice). I estimate that there is a 50-50 chance of a recount. We might not know the exact outcome for some time.
The next-closest state is North Carolina, with margin of Romney +1.0%. All other margins are 2% or greater.
POPULAR VOTE. Using the above Meta-Margin for the last three days was Obama +2.76%. The median of national polls is Obama +1.0 +/- 0.4% (n=21 polls). The approach I described before for combining these measures gives
- Final predicted popular-vote margin: Obama +2.2 +/- 1.0%.
- Two-candidate vote share: Obama 51.1%, Romney 48.9%.
- Allowing 1% for minor-party candidates: Obama 50.6%, Romney 48.4%.
Finally, here is the EV histogram based on the optimized probabilities. The two highest peaks correspond to FL-Romney and FL-Obama.
By 5:00pm I’ll have some graphs for you to print. They will let you compare the returns with polls.