The idea behind political prediction markets is simple. Lots of people wager on the outcome of political campaigns: Who’s going to be the Democratic presidential nominee? Will the Republicans take back the House? And when the votes are counted, the winning bettors collect. The thrill of prediction markets for political junkies is that they harness “the wisdom of crowds.” A single person’s bet on an election outcome isn’t very good, but thousands of bets, with real stakes, are more likely to predict the correct result than even the best pundit. The Iowa Electronic Markets, the big daddy of the political prediction markets, is consistently better at forecasting winners than pre-election polls.