The Marketcast Method for Aggregating Prediction Market Forecasts

We describe a hybrid forecasting method called marketcast. Marketcasts are based on bid and ask orders from prediction markets, aggregated using techniques associated with survey methods, rather than market matching algorithms. We discuss the process of conversion from market orders to probability estimates, and simple aggregation methods. The performance of marketcasts is compared to a traditional prediction market and a traditional opinion poll. Overall, marketcasts perform approximately as well as prediction markets and opinion poll methods on most questions, and performance is stable across model specifications.