Polly collects daily forecasts from the vote-share market of the Iowa Electronic Markets (IEM) for forecasting the 2012 U.S. presidential election. On this prediction market, participants can bet real-money on what will be the election outcome.

Polly then uses the daily IEM forecasts and calculates a 7-day rolling average. 

The time-series chart below shows how the combined IEM forecast has evolved over time.