In my previous post, I looked at some of the reasons why we are so useless at making economic predictions, and some of the ideas for what might be done about it. One of the key problems, raised by Nassim Nicholas Taleb most recently in his book Antifragile, is the absence of skin in the game, ie forecasters having something to lose if their forecasts are wildly off.
But what if all forecasters had to have something to lose before they were allowed to make forecasts? What if every IMF or OBR forecast came with a bill if it was seriously adrift? What if you knew whenever you read a forecast in a newspaper or on a television screen that the person making that forecast had invested something in their belief in their own forecast?
Betting on events dates back at least to the 16th century, but prediction markets (also known as predictive markets, information markets, decision markets, idea futures, event derivatives, or virtual markets) have developed most strongly over the last 25 years or so (the University of Iowa launched its first electronic market as an experiment in 1988). Intrade, which describes itself as the world’s leading prediction market, is now a little smaller than it was following the news just before Christmas last year that it would no longer let Americans trade on its site. It had been sued by the US regulator of the commodities derivative markets for breaking a commitment not to allow trading on the constituents of those markets.
A paper on prediction markets earlier this year called Prediction Markets for Economic Forecasting by Snowberg, Wolfers and Zitzewitz suggests there are 3 main types:
· Winner takes all. If the event you have bet on happens you win. If not, you lose your stake. Intrade is this type of prediction market: you pay a proportion of £10 a share based on the average probability of the event happening (according to the market participants) and get £10 back if it happens, nothing if it doesn’t. The Iowa Electronic Market current offerings, on congressional elections and US federal monetary policy, are also winner takes all. The price of the bet at any time should reflect the market’s view of the probability of the event happening.
· Index. The amount paid out is unknown but tied to the variable you are betting on, eg the number of seats won by a party in a particular parliamentary election, or the value of an index at close of business on a particular date. The price of the bet at any time should reflect the market’s view of the expected value of the outcome.
· Spread betting. Most commonly found on sports betting sites, the amount bet and the amount paid out are fixed, but the event that leads to a pay out (eg number of goals scored in a match more than x) changes until the numbers of buys and sells match (a “buy” in this example is betting the number of goals will be above x, a “sell” is betting the number of goals will be below y, a number less than x. The spread, on which the betting site makes its money, is the difference between x and y. This could equally be applied to the values of an index at a particular date (eg Spreadex offer just such bets on several major share indices as well as currency exchange rates). Depending on the relationship between the pay out and the bet, the value of the spread points at any time should reflect the market’s view of a particular point in the probability distribution of the event, eg if the pay out is twice the bet, this would be the median (ie a 50% chance of the outcome being higher or lower).
As we saw in my previous post, currently economic predictions are largely blown off course by either:
- Over-confidence in the information used to make them; or
- The difficulty in standing out against a market which is making everyone a lot of money (buying has limited downside, selling limited upside); or (another possibility I haven’t mentioned before)
- Bias in individual “expert” judgements, eg those with reputations at stake may want to keep their assumptions somewhere in the middle of the pack rather than standing out most of the time as this is less risky (hence the obsession with “benchmarking” assumptions in the actuarial world for instance).
Prediction markets can help with all of these problems:
- Having to bet on your opinion should cause you to weigh the evidence backing it more carefully. Also, once a market is established and attracting a lot of bets, the range of evidence on which opinions are being based should expand. Prediction markets also appear to be quite difficult to manipulate or arbitrage.
- Prediction markets can respond very rapidly to changes in the information available. As an example, within 25 minutes of Donald Rumsfeld’s former chief of staff tweeting about the death of Osama Bin Laden, the market view of the probability of this event on a prediction market rose from 7% to 99%.
- Betting can take place anonymously. So, although the betting site knows who you are, no one else does, and the data from the voting therefore gets out into the public domain without any individual being accused of talking down a market or risking their reputation.
For these reasons, amongst others, forecast accuracy for established prediction markets might be expected to outperform that of professional forecasters. The paper of Wolfers et al suggests that this is the case.
There are still problems. The markets need to be popular to be much use for predictions, so the questions need to be interesting enough for mass participation. Secondly, a market could theoretically be undermined (although not necessarily to the detriment of its predictive ability) by traders with inside information. However, there are quite a few safeguards in place against this type of activity. Intrade, for instance, requires a photo ID and two proofs of address before it registers anyone to trade on their site. And Spreadex are regulated by the Financial Conduct Authority. A third problem is referred to as the “longshot bias”, which is observed on all types of betting markets. People tend to over-bet on events with long odds against them and under-bet on events which are fairly likely (which explains the narrowing of the odds as the starting gun approached on that horse you bet on just because of its name in the Grand National a couple of months ago). This is a problem of the winner takes all type of market, seemingly related to behavioural factors around the difference between how we view winning and losing, and it is difficult to see how it could be avoided completely. Care may need to be taken therefore when interpreting prediction markets on events which are seen as having fairly low probabilities.
But overall, prediction markets would seem to offer a way of significantly improving economic predictions, so why not make them compulsory for people who want to make such forecasts? By putting a cost on such predictions (a minimum bet could be set based on the size of the organisation making it), it would remove the casual forecasting we currently see too much of, and encourage people to review their beliefs rather more carefully. It would also ensure that the markets were popular enough to be effective. It may be that economic forecasting will always be far from perfect, but this seems a good place to start if we want, in Nate Silver’s words, to be “less and less and less wrong”.
A tax on economists? Not at all. But it might mean that we all have skin in the right game.