"If the expected happens, what have we learned? Let’s start by asking what we can say before

any election returns are in. Obama is expected to win the national popular vote by 4.8

percentage points, with an expected electoral vote total of 340 (compared to 270 needed for

victory), and a 96% chance of winning the electoral vote (with a 0.2% chance of a tie in the

electoral college). The top row of Figure 1 shows the forecast distributions of Obama’s popular

and electoral vote shares.

Now, what if the vote margin in Virginia, Indiana, Georgia, South Carolina, and Kentucky were

to equal the expected -5.7%? We pipe this assumption through our model by calculating, for

each of our 10,000 simulations, the average vote margin in these five states, and then restricting

our analysis to the subset of simulations for which this vote margin is within 1 percentage point

of its expected value (that is, between -6.7% and -4.7%). Out of our 10,000 simulations, 2800

fall in this range; that is, we predict there is a 28% chance that McCain’s average vote margin in

these five states will be between 4.7% and 6.7%. What is of more interest is what happens if this

occurs. Considering this subset of simulations, Obama’s expected national popular vote margin

is +4.7%, his expected electoral vote total is 343, and the conditional probability of an Obama

victory is 100%: he wins the electoral college in all 2800 simulations in this condition."