预测市场（Prediction Markets）

如果你想要预测一个未来事件的结果，例如世界杯的冠军，下一任美国总统，或是今年诺贝尔经济学奖/图灵奖会花落谁家，甚至是今天的课程是否会留作业，你可以问一个值得信赖的专家，但专家可能不会告诉你他的真实想法，或者你需要支付高昂的费用。因此我们可以思考另一种方式：

预测市场是人们可以交易基于未知未来事件结果支付的合约的市场，这些合约产生的市场价格可以理解为市场参与者之间的一种集体预测，这些价格是基于个人的期望和投资者为这些期望投入资金的意愿。预测市场类似于商品或其他金融资产价格的期货市场。在期货市场中，交易者根据他们对标的资产未来价格的预期来提高或降低期货合约的价格。预测市场只是期货市场，其中交易的未来事件不是未来某个时间点的资产价格。预测市场涉及一群人对各种事件进行投机——交易平均值、选举结果、季度销售结果，甚至电影总收入。

Richard Roll, Orange Juice and Weather, The American Economic Review, Vol. 74, No. 5 (Dec., 1984), pp. 861-880 (20 pages)

爱荷华州电子市场（由爱荷华大学亨利 B. 蒂皮商学院的教员运营）是运营中最著名的预测市场之一。

期货与期权

https://www.investopedia.com/terms/p/prediction-market.asp

What Is a Prediction Market? A prediction market is a market where people can trade contracts that pay based on the outcomes of unknown future events. The market prices generated from these contracts can be understood as a kind of collective prediction among market participants. These prices are based on the individual expectations and willingness of investors to put their money on the line for those expectations.

The Iowa Electronic Markets (operated by faculty at the University of Iowa Henry B. Tippie College of Business) are among the better-known prediction markets in operation. 1

KEY TAKEAWAYS Prediction markets are markets where contracts that are contingent on the occurrence of events in the future can be traded. These contracts are similar to bets on uncertain events, and prediction markets are also known as betting markets. They are used to bet on a variety of instances and circumstances, from the outcome of presidential elections to the results of a sporting event. Prediction markets depend on scale; the more individuals participate in the market, the more data there is, and the more effective they become. The Iowa Electronic Markets and PredictIt are both well-known examples of prediction markets. Understanding a Prediction Market Prediction markets are similar to futures markets for commodities or other financial asset prices. In futures markets, traders bid up or down the price of a future contract based on their expectation of what the future price of the underlying asset will be. Prediction markets are just futures markets where the future event being traded upon is something other than the price of an asset at some point in the future. Prediction markets involve a collection of people speculating on a variety of events—exchange averages, election results, quarterly sales results, or even gross movie receipts.

Robin Hanson, a professor at George Mason University, is an advocate of prediction markets. He makes the case for prediction markets by emphasizing the removal of reliance on self-interested punditry by so-called experts. "Instead, let us create betting markets on most controversial questions, and treat the current market odds as our best expert consensus. The real experts (maybe you), would then be rewarded for their contributions, while clueless pundits would learn to stay away," Hanson says on his web page. 2

The price in a prediction market is a bet that a particular event will occur. It also represents an estimated value that the person placing the bet assigns to the parameters being considered in the bet. Unlike public markets, where bets are placed indirectly on intangibles, such as government policy or the possible outcomes of an election (via the effects these things are expected to have on asset prices), prediction markets enable users to bet directly on a piece of information that they believe is valuable.

For example, it is impossible for a speculator to bet directly on an election in the U.S. Instead, the trader will have to find stocks that might increase in value if a certain candidate is elected. However, prediction markets allow traders to bet directly on the possibility of actual candidates being elected to office.

The oldest online prediction market is the Iowa Electronic Markets, run by the University of Iowa. Launched in 1988, it has been used to forecast the results of presidential elections with greater accuracy than traditional opinion polls. 1

Uses of Prediction Markets Because they represent a wide variety of thoughts and opinions—much like the markets as a whole—prediction markets have proven to be quite effective as a prognostic tool. As a result of their visionary value, prediction markets (sometimes referred to as virtual markets) have been utilized by a number of large companies.

The blending of economics, politics, and more recently, cultural factors, has only made the demand for prediction even greater. Add the benefits of data analytics and artificial intelligence; we're living in the golden age of data and statistical utility.

Over the past 50 years, prediction markets have moved from the private domain to the public. Prediction markets can be thought of as belonging to the more general concept of crowdsourcing. Crowdsourcing is specifically designed to aggregate information on particular topics of interest. The main purpose of prediction markets is eliciting aggregating beliefs over an unknown future outcome. Traders with different beliefs trade on contracts whose payoffs are related to the unknown future outcome; the market prices of the contracts are considered as the aggregated belief.

In theory, by pulling information from every available source, estimation methods should improve and become more accurate and consistent. In reality, as we're currently learning, data manipulation brings a host of new ethical and human biases. As leaders of all varieties help everyday individuals trust and appreciate prediction markets, their use and effectiveness will only improve further.

Types of Prediction Markets There are several models for prediction markets, depending on the mechanism and frequency of forecasting.

Continuous Double Auction A continuous double auction is a type of trading mechanism to match buyers to sellers, much like the stock market. In the case of prediction markets, traders can buy or sell their bets on a certain outcome, with the price rising or falling if that outcome appears more or less likely. This requires the operator of the prediction market to maintain a ledger of each trade, delivering the payoff to the final owner of each bet.

Automated Market Makers An automated market maker is used to provide liquidity for markets where there may not be enough buyers or sellers. In this system, the operator of the prediction market acts as a counterparty to all trades, similar to the "house" in a casino. With each trade, the operator can adjust the payoffs, based on the number of bets placed on each outcome. This system is commonly used in sports betting.

Play Money Markets While most prediction markets rely on using real money to incentivize accurate forecasts, this can run into trouble in jurisdictions where online gambling is illegal. Some prediction markets allow trades in virtual tokens instead of money, with prizes or other incentives to players that collect the most tokens. This allows markets to operate legally, while providing a low-risk platform for traders.

Blockchain-Based Prediction Markets Developments in blockchain technology have enabled the creation of decentralized prediction markets that can operate without being controlled by a single party or operator. Typically, these markets use smart contracts to mediate bets between different traders, and a complex voting system to determine the final outcome.

Decentralized prediction markets have attracted controversy, both for ethical reasons and the possibility of manipulation. Augur, one of the first decentralized prediction markets, became infamous after traders began betting on the deaths of political figures, raising the possibility that it might become an "assassination market." 3

Other Crowdsourcing Methods There are also less formal ways to crowdsource forecasting, such as opinion polls or betting without rewards. These options offer a convenient way to collect crowd forecasts, without a financial incentive for correct forecasting.

Benefits of Prediction Markets Although they are sometimes controversial, the advantage of prediction markets is that they can benefit from the wisdom of crowds. By collecting and weighing the predictions of a large number of traders, they can provide a market-wide forecast that is generally more reliable and balanced than any single expert opinion. The potential payoffs incentivize traders to reach accurate predictions.

Many real-world securities are traded with the same mechanism as bets in a prediction market. Binary options trades represent a bet on the likelihood of a real-world event, with the price rising or falling as the likelihood of each outcome changes. Prediction markets raise ethical questions as well as legal ones. One of the latest online markets is the blockchain-based Augur, whose betting pools were described as an "assassination market." 3 Real-World Example of Prediction Markets One of the pioneers of online predictions markets is the Iowa Electronic Market (IEM), an experiment in market-based forecasting run by faculty of the University of Iowa's Tippie School of Business. Using real money, speculators on the IEM have been able to forecast the outcome of presidential elections with greater long-run accuracy than traditional opinion polls. 1

The IEM is not regulated by either the CFTC or the SEC, and regulators have issued two no-action letters stating that they would not attempt to regulate it. This was due to the academic nature of the IEM, and the fact that it is not operated for profit. 4

What Role Do Prediction Markets Play in Economics? Prediction markets can be used to create crowd-sourced forecasts, collecting predictions from dozens or hundreds of traders rather than a handful of experts. Traders "vote" by placing bets on what they believe is the most likely outcome, thereby causing the price of that outcome to rise or fall. This market mechanism effectively turns the share price for each outcome into a crowdsourced estimate of that outcome's probability.