Presidential Election Statistics

I've played around with different ways for predicting presidential elections in the past, but recently I started thinking in a different way. One reason for is that I found that when I applied my methods for predicting elections, it produced no more accurate results than just assuming the following election was exactly the same as the previous.

With that in mind, I decided to look at past elections and based on historic swings in the vote, come up with a prediction for the chances a particular state will vote for a particular party. On average, the swing between Republican and Democrat is 8.6%, with a standard deviation of 6.6%. To put it another way, 95% of the time, the vote swing in any individual state is between 0 percentage points and 21.5 percentage points. What this means is that, if one party won a state by more than 21.5% last election, the chances that it will vote for a different party next election is less than 5%.

Based on the 2008 results, I created a map. It's a bit messy, but should be easy enough to figure out. The colors represent the party most likely to win that particular state and darkness of the colors corresponds to the chances that party will win that state assuming the 2012 result is totally random.

Looking at just the darkest states, those at a 99% confidence level, one should notice something. Some of the darkest blue states are really big, but the darkest red states are all rather small (in population at least). Democrats have done very well recently in the most populous states. An election could be won with just the 11 largest states. Of those, Obama won 9 in the last election. Basically, no matter what happens in 2012, Democrats are virtually guaranteed to win 149 electoral votes (out of 270 needed to win) and 3 of the 11 largest states. On the other hand, Republicans are only guaranteed 20 electoral votes. From the states that the Republicans have more than a 90% chance of winning, they only get 76 electoral votes, which is less than California and New York combined. Of the big states, Republicans only have an 84% chance of keeping Texas and a 65% chance of keeping Georgia. Basically, Democrats are going into the 2012 election with a huge built in lead. Also, since Democrats have such a commanding lead in the large states, they need to defend and win fewer states.

Of course, 2008 was a massive victory for the Democrats, so it seems unlikely that they will maintain the same level of support. Therefore the 2012 result won't be completely random, there will most likely be a swing to the right. So let's assume that there is an average 8.6% swing to the right.

Suddenly, a lot of states become solidly Republican, however, they reveal a weakness. Democrats still win 3 big states with 99% confidence while Republicans only win 1 big state. Even though Republicans win 19 states with 99% confidence compared to Democrats' 9 plus DC those 19 states only represent 155 electoral votes compared to 142 for the Democrats. Basically, even assuming that every state swings to the right, Republicans aren't guaranteed a win as the Democrats have too much solid support from California, Illinois, and New York.

In order for Republicans to have a solid lead over the Democrats in the electoral college, there would have to be a uniform swing to the right in excess of 9%. What's intriguing about that, is that with a 9% national swing, the Republican candidate would win 55% of the popular vote. This potentially means that in 2012, if the Republican candidate wins between 50% and 55% of the popular vote, they risk losing the electoral college.