Scientists are beginning to understand why these ‘mini Wall Streets’ work so well at forecasting election results — and how they sometimes fail. ... Experiments such as this are a testament to the power of prediction markets to turn individuals’ guesses into forecasts of sometimes startling accuracy. That uncanny ability ensures that during every US presidential election, voters avidly follow the standings for their favoured candidates on exchanges such as Betfair and the Iowa Electronic Markets (IEM). But prediction markets are increasingly being used to make forecasts of all kinds, on everything from the outcomes of sporting events to the results of business decisions. Advocates maintain that they allow people to aggregate information without the biases that plague traditional forecasting methods, such as polls or expert analysis. ... sceptics point out that prediction markets are far from infallible. ... prediction-market supporters argue that even imperfect forecasts can be helpful. ... People have been betting on future events for as long as they have played sports and raced horses. But in the latter half of the nineteenth century, US efforts to set betting odds through marketplace supply and demand became centralized on Wall Street, where wealthy New York City businessmen and entertainers were using informal markets to bet on US elections as far back as 1868. ... Friedrich Hayek. He argued that markets in general could be viewed as mechanisms for collecting vast amounts of information held by individuals and synthesizing it into a useful data point — namely the price that people are willing to pay for goods or services.