Predicting the 2012 US Presidential Election - The Day After
In our paper prepared for APSA 2012 (Here) we used Ensemble Bayesian Model Averaging to combine 9 prominent political science forecasting model into a single prediction for the 2012 presidential election. The EBMA prediction was based on the track record of these models in the past and their 2012 forecast.
Our model predicted 50.48% of the two party popular vote for President Obama. And while that is just about right on for the popular vote percentage, it is under by 7/10 of a percent from the current figures, which give President Obama 51.2% of the two-party popular vote (Results still changing, November 8, 11:00 am EST).
The EBMA model places a lot of weight on the prediction generated by Professor Alan Abramowitz, and we’d do a lot worse without his model in the ensemble. We are likely to have under predicted President Obama's vote share because most of the models did under predict, especially those favoring a Romney victory. Both of these factors drew our aggregate prediction below what actually occurred. But not by too much.
It is now very clear that the ensemble aggregation approach, applied to polls by Drew Linzer and Simon Jackman, among others, did very well in predicting the outcome in terms of state results and electoral votes--even if one looks at their results from last summer, ignoring election eve updates.