1. About the project
2. PollyVote method
While combining is useful whenever more than one forecasts for the outcome are available, the approach is particularly valuable if
- Many forecasts from evidence-based methods are available.
- The forecasts draw upon different methods and data.
- There is uncertainty about which method is most accurate.
These conditions perfectly apply to election forecasting. First,there are many evidence-based methods for predicting election outcomes. Second, these methods often rely on different data. Third, in most situations, it is difficult to determine a priori which method will provide the best forecast at a given time in an election cycle.
3. Forecast accuracy
The PollyVote published forecasts prior to each of the three U.S. presidential elections. In addition, one ex post analysis tested how a the PollyVote would have performed for the three elections from 1992 to 2000. Across the last 100 days prior to election day, the PollyVote provided more accurate forecasts than each of the component methods (Graefe et al. 2014b). Error reductions were large. For example, compared to single polls, the PollyVote reduced the forecast error by 59%. Comparisons have also been made with other methods. For example, forecasts of the 2012 election were also substantially more accurate than the closely watched forecasts at FiveThirtyEight.com (Graefe et al. 2014a).
The 2004 PollyVote was launched in March 2004 and forecast a victory for President Bush over the 8 months that it was making forecasts. The final forecast published on the morning of the election predicted that President would receive 51.5% of the popular two-party vote, an error of 0.3 percentage points (Cuzán et al. 2005).
The 2008 PollyVote was launched in August 2007 and forecast a victory for Barack Obama over the 14 months that it was making daily forecasts. On Election Eve, it predicted that Obama would receive 53.0% of the popular two-party vote, an error of 0.7 percentage points (Graefe et al. 2009).
The 2012 PollyVote was launched in January 2011 and forecast a victory for President Obama over the 22 months that it was making daily forecasts. On Election Eve, it predicted that Obama would receive 51.0% of the popular two-party vote, an error of 0.9 percentage points (Graefe et al. 2014a).