The paradoxical efficient market hypothesis (2024)
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The paradoxical efficient market hypothesis (2024)
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Re: The paradoxical efficient market hypothesis (2024)
#2For this paradox to function, information would have to be static, unless I'm missing something.
Re: The paradoxical efficient market hypothesis (2024)
#3This seems to be a case of a feedback loop creating emergent behavior.
Let's say almost everyone believed in the Efficient Market Hypothesis (EMH). Then, trading would decrease significantly, since most people would think that stocks are already fairly priced. That means the few people who trade would move the market significantly, based on whatever idiosyncratic value-theories they had.
But then the EMH believers would see wild moves in the market and stop believing in EMH. They would start trading more to gain profits.
And as more traders participated, the market would behave more and more like the EMH were true. Eventually, the market would stabilize. Prices wouldn't swing so much. This would increase the number of EMH believers.
It would be interesting to survey belief in EMH among traders. If my model is correct, the percentage of EMH believers should be roughly constant, or at least oscillate around some optimum value.
Re: The paradoxical efficient market hypothesis (2024)
#4The EMH is a description of how the market behaves when a sufficiently large number of independent actors are looking for alpha. It is not a prescription of how the market should behave.
The conclusion is that with a sufficiently large number of actors in the market all seeking profits by trying to find misevaluation of stock prices, the excess profits of any individual actor will (assuming they all have access to the same information) converge to zero.
Its less a paradox and more a matter of game theory. Every investment firm which gives up trying to look for alpha (believing it is fruitless) means the remaining firms have more opportunities to find stocks with available information not reflected in the price. There's no paradox here: each individual actor is incentivized to participate in order to not miss out on that potential for excess profits, and the net effect is the EMH.
Re: The paradoxical efficient market hypothesis (2024)
#5For this paradox to function, information would have to be static, unless I'm missing something.
Also wouldn’t all information have to be available to all participants? How does insider knowledge factor here (because it sure does in the market)
Re: The paradoxical efficient market hypothesis (2024)
#6See also:
> The Grossman-Stiglitz Paradox is a paradox introduced by Sanford J. Grossman and Joseph Stiglitz in a joint publication in American Economic Review in 1980[1] that argues perfectly informationally efficient markets are an impossibility since, if prices perfectly reflected available information, there is no profit to gathering information, in which case there would be little reason to trade and markets would eventually collapse.[2]
* https://en.wikipedia.org/wiki/Grossman-Stiglitz_paradox
So the more efficient markets are, the hard it will be to find "alpha" (returns), and so more people will stop trying. But as more people stop trying, markets will become more inefficient, in which case people can find alpha again, which encourages more participants.
Re: The paradoxical efficient market hypothesis (2024)
#7Anyone who has lived through a market correction (the tariff announcements in early April this year being a recent example, though there have been far worse) should be able to see that market prices do not always accurately reflect even the consensus view of value (which itself can be wrong). As people are forced to de-lever, everything goes down at once, often by very similar amounts, even though it cannot be possible that everything suddenly lost the same amount of value simultaneously.
To quote Richard Bookstaber, "The principal reason for intraday price movement is the demand for liquidity... the role of the market is to provide immediacy for liquidity demanders. ...market crises... are the times when liquidity and immediacy matter most. ...the defining characteristic is that time is more important than price. ...diversification strategies fail. Assets that are uncorrelated suddenly become highly correlated, and all positions go down together. The reason for the lack of diversification is that in a high-energy market, all assets in fact are the same.... What matters is who holds the assets." (from A Framework for Understanding Market Crises, 1999)
Was the market drop an accurate reflection of the value that would have been destroyed by those tariffs, discounted by the probability that they would have been enacted as drafted? Nobody knew then, and I maintain that nobody even knows now. That was not the calculation that was being made.
Re: The paradoxical efficient market hypothesis (2024)
#8See also: > The Grossman-Stiglitz Paradox is a paradox introduced by Sanford J. Grossman and Joseph Stiglitz in a joint publication in American Economic Review in 1980[1] that argues perfectly informationally efficient markets are an impossibility since, if prices perfectly reflected available information, there is no profit to gathering information, in which case there would be little reason to trade and markets wou…
Turnips and Carrots could be priced equally per tonne, and still be worth trading because although you might think all root vegetables are substitutable, it turns out you can't make carrot soup with Turnips.
It's always worth remembering trade involves use values as well. We don't only trade for asymmetric profit, and there are things like hedging which include a yield where both can acknowledge future risk, and price accordingly.
I'm probably ignorant of some magic economist reason why the words are fluid and don't mean what I think they mean: this always seems to be the case talking economics from the stuffed armchair.
Another take on this is that we can agree to facts and disagree to consequences. Same information, different conclusions.
Re: The paradoxical efficient market hypothesis (2024)
#9The EMH is a description of how the market behaves when a sufficiently large number of independent actors are looking for alpha. It is not a prescription of how the market should behave. The conclusion is that with a sufficiently large number of actors in the market all seeking profits by trying to find misevaluation of stock prices, the excess profits of any individual actor will (assuming they all have access to th…
Yeah, I think the "paradox" is usually a problem for pundits and academics and not practitioners. Lots of people have experience finding and correcting market inefficiencies, usually getting paid for it.
Re: The paradoxical efficient market hypothesis (2024)
#10 the hypothesis maintains that
stock prices reflect all relevant
information about the stock
What if it takes 12 months of hard thinking to draw the right conclusion from the information? Are there many investors who go to such lengths? Are they all thinking at the same speed? And if not, what does that tell us about the EMH?
Google released DeepDream in 2015. My feeling is that with enough thinking, one could have predicted where image generation is going in the next decade and that language generation would go a similar route. And that this will lead to a high demand in Nvidia's GPUs. But that thinking would not be instantly. It would take months or years.