Tag Archive for 'Efficient market hypothesis'


Defending the EMH

Tim Harford has gone in to bat for the Efficient Market Hypothesis (EMH).  As Tim says, somebody has to.

Sort-of-officially, there are three versions of the EMH:

  • The strong version says that the market-determined price is always “correct”, fully reflecting all public and private information available to everybody, everywhere.
  • The semi-strong version says that the price incorporates all public information, past and present, but that inside information or innovative analysis may produce a valuation that differs from that price.
  • The weak version says that the price incorporates, at the least, all public information revealed in the past, so that looking at past information cannot allow you to predict the future price.

I would add a fourth version:

  • A very-weak version, saying that even if the future path of prices is somewhat predictable from past and present public information, you can’t beat the market on average without some sort of private advantage such as inside information or sufficient size as to allow market-moving trades.

    For example, you might be able to see that there’s a bubble and reasonably predict that prices will fall, but that doesn’t create an opportunity for market-beating profits on average, because you cannot know how long it will be before the bubble bursts and, to regurgitate John M. Keynes, the market can remain irrational longer than you can remain solvent.

I think that almost every economist and financial analyst under the sun would agree that the strong version is not true, or very rarely true.  There’s some evidence for the semi-strong or weak versions in some markets, at least most of the time, although behavioural finance has pretty clearly shown how they can fail.  The very-weak version, I contend, is probably close to always true for any sufficiently liquid market.

But looking for concrete evidence one way or another, while crucially important, is not the end of it.  There are, more broadly, the questions of (a) how closely each version of the EMH approximates reality; and (b) how costly a deviation of reality from the EMH would be for somebody using the EMH as their guide.

The answer to (a) is that the deviation of reality from the EMH can be economically significant over short time frames (up to days) for the weak forms of the EMH and over extremely long time frames (up to years) for the strong versions.

The answer to (b), however, depends on who is doing the asking and which version of the EMH is relevant for them.  For retail investors (i.e. you and me, for whom the appropriate form is the very-weak version) and indeed, for most businesses, the answer to (b) is “not really much at all”.  This is why Tim Harford finishes his piece with this:

I remain convinced that the efficient markets hypothesis should be a lodestar for ordinary investors. It suggests the following strategy: choose a range of shares or low-cost index trackers and invest in them gradually without trying to be too clever.

For regulators of the Too-Big-To-Fail financial players, of course, the answer to (b) is “the cost increases exponentially with the deviation”.

The failure of regulators, therefore, was a combination of treating the answer to (a) for the weak versions as applying to the strong versions as well; and of acting as though the answer to (b) was the same for everybody.  Tim quotes Matthew Bishop — co-author with Michael Green of “The Road from Ruin” and New York Bureau Chief of The Economist — as arguing that this failure helped fuel the financial crisis for three reasons:

First, it seduced Alan Greenspan into believing either that bubbles never happened, or that if they did there was no hope that the Federal Reserve could spot them and intervene. Second, the EMH motivated “mark-to-market” accounting rules, which put banks in an impossible situation when prices for their assets evaporated. Third, the EMH encouraged the view that executives could not manipulate the share prices of their companies, so it was perfectly reasonable to use stock options for executive pay.

I agree with all of those, but remain wary about stepping away from mark-to-market.


The Nobel committee can’t lose in their decision over Fama

Alex Tabarrok points out the amusing truth:

Ladbrokes gives Eugene Fama the best odds for winning the economics Nobel.  Thus, if Fama wins he will have deserved to have won and if Fama loses he will not have deserved to have won.  The Nobel committee cannot go wrong no matter what it does!  Think about it.


How to value toxic assets (part 6)

Via Tyler Cowen, I am reminded (again) that I should really be reading Steve Waldman more often.  Like, all the time.  After reading John Hempton’s piece that I highlighted last time, Waldman writes, as an afterthought:

There’s another way to generate price transparency and liquidity for all the alphabet soup assets buried on bank balance sheets that would require no government lending or taxpayer risk-taking at all. Take all the ABS and CDOs and whatchamahaveyous, divvy all tranches into $100 par value claims, put all extant information about the securities on a website, give ’em a ticker symbol, and put ’em on an exchange. I know it’s out of fashion in a world ruined by hedge funds and 401-Ks and the unbearable orthodoxy of index investing. But I have a great deal of respect for that much maligned and nearly extinct species, the individual investor actively managing her own account. Individual investors screw up, but they are never too big to fail. When things go wrong, they take their lumps and move along. And despite everything the professionals tell you, a lot of smart and interested amateurs could build portfolios that match or beat the managers upon whose conflicted hands they have been persuaded to rely. Nothing generates a market price like a sea of independent minds making thousands of small trades, back and forth and back and forth.

I don’t really expect anybody to believe me, but I’ve been thinking something similar.

CDOs, CDOs-squared and all the rest are derrivatives that are traded over the counter; that is, they are traded entirely privately.  If bank B sells some to hedge fund Y, nobody else finds out any details of the trade or even that the trade took place.  The closest we come is that when bank B announces their quarterly accounts, we might realise that they off-loaded some assets.

On the more popularly known stock and bond markets, buyers publicly post their “bid” prices and sellers post their “ask” prices. When the prices meet, a trade occurs.[*1] Most details of the trade are then made public – the price(s), the volume, the particular details of the asset (ordinary shares in XXX, 2-year senior notes from XXX with an expiry of xx/xx/xxxx, etc) – everything except the identity of the buyer and seller. Those details then provide some information to everybody watching on how the buyer and seller value the asset. Other market players can then combine that with their own private valuations and update their own bid or ask prices accordingly. In short, the market aggregates information. [*2]

When assets are traded over the counter (OTC), each participant can only operate on their private valuation. There is no way for the market to aggregate information in that situation. Individual banks might still partially aggregate information by making a lot of trades with a lot of other institutions, since each time they trade they discover a bound on the valuation of the other party (an upper bound when you’re buying and the other party is selling, a lower bound when you’re selling and they’re buying).

To me, this is a huge failure of regulation. A market where information is not publicly and freely available is an inefficient market, and worse, one that expressly creates an incentive for market participants to confuse, conflate, bamboozle and then exploit the ignorant. Information is a true public good.

On that basis, here is my idea:

Introduce new regulation that every financial institution that wants to get support from the government must anonymously publish all details of every trade that they’re party to. The asset type, the quantity, the price, any time options on the deal, everything except the identity of the parties involved. Furthermore, the regulation would be retroactive for X months (say, two years, so that we get data that predates the crisis).  On top of that, the regulation would require that every future trade from everyone (whether they were receiving government assistance or not) would be subject to the same requirementes.  Then everything acts pretty much like the stock and bond markets.

The latest edition of The Economist has an article effectively questioning whether this is such a good idea.

[T]ransparency and liquidity are close relatives. One enemy of liquidity is “asymmetric information”. To illustrate this, look at a variation of the “Market for Lemons” identified by George Akerlof, a Nobel-prize-winning economist, in 1970. Suppose that a wine connoisseur and Joe Sixpack are haggling over the price of the 1998 Château Pétrus, which Joe recently inherited from his rich uncle. If Joe and the connoisseur only know that it is a red wine, they may strike a deal. They are equally uninformed. If vintage, region and grape are disclosed, Joe, fearing he will be taken for a ride, may refuse to sell. In financial markets, similarly, there are sophisticated and unsophisticated investors, and unless they have symmetrical information, liquidity can dry up. Unfortunately transparency may reduce liquidity. Symmetry, not the amount of information, matters.

I’m completely okay with this. Symmetric access to information and symmetric understanding of that information is the ideal. From the first paragraph and then the last paragraph :

… Not long ago the cheerleaders of opacity were the loudest. Without privacy, they argued, financial entrepreneurs would be unable to capture the full value of their trading strategies and other ingenious intellectual property. Forcing them to disclose information would impair their incentive to uncover and correct market inefficiencies, to the detriment of all …

Still, for all its difficulties, transparency is usually better than the alternative. The opaque innovations of the recent past, rather than eliminating market inefficiencies, unintentionally created systemic risks. The important point is that financial markets are not created equal: they may require different levels of disclosure. Liquidity in the stockmarket, for example, thrives on differences of opinion about the value of a firm; information fuels the debate. The money markets rely more on trust than transparency because transactions are so quick that there is little time to assess information. The problem with hedge funds is that a lack of information hinders outsiders’ ability to measure their contribution to systemic risk. A possible solution would be to impose delayed disclosure, which would allow the funds to profit from their strategies, provide data for experts to sift through, and allay fears about the legality of their activities. Transparency, like sunlight, needs to be looked at carefully.

This strikes me as being around the wrong way.  Money markets don’t rely on trust because their transactions are so fast; their transactions are so fast because they’re built on trust.  The scale of the crisis can be blamed, in no small measure, because of the breakdown in that trust.

I also do not buy the idea of opacity begetting market efficiency.  It makes no sense.  The only way that information disclosure can remove the incentive to “uncover and correct” inefficiencies in the market is if by making the information public you reduce the inefficiency.  I’m not suggesting that we force market participants to reveal what they discover before they get the chance to act on it.  I’m only suggesting that the details of their action should be public.

[*1] Okay, it’s not exactly like that, but it’s close enough.

[*2] Note that information aggregation does not necessarily imply that the Efficient Market Hypothesis (EMH), but the EMH requires information aggregation to work.

Other posts in this series:  1, 2, 3, 4, 5, [6].


Believing the “experts”

One of my favourite topics – indeed, in a way, the basis of my current research – is looking at how we tend to accept the declarations of other people as true without bothering to think on the issue for ourselves.  This is often a perfectly rational thing to do, as thinking carefully about things is both difficult and time consuming, often resulting in several possible answers that serve to increase our confusion, not lessen it.  If we can find somebody we trust to do the thinking for us and then tell us their conclusions, that can leave us free to put our time to work in other areas.

The trick is in that “trust” component.  To my mind, we not only tend to accept the views of people widely accepted to be experts, but also of anybody that we believe knows more than us on the topic.  This is one of the key reasons why I am not convinced by the “wisdom of crowds” theory and it’s big brother in financial markets, the efficient market hypothesis. I’m happy to accept that they might work when individual opinions are independent of each other, but they rarely are.

Via Greg Mankiw, I’ve just discovered a fantastic example of a person who is not an expert on a topic, but definitely more knowledgeable than most people, who nevertheless got something entirely wrong.  The person is Mark Hulbert, who is no slouch in the commentary department. Here is his article over at MarketWatch:

I had argued in previous columns that inflation might not be heating up, despite evidence to the contrary from lots of different sources …

I had based my argument on the narrowing yield spread between regular Treasury bonds and the special type of Treasuries known as TIPS. The only apparent difference between these two kinds of Treasury securities is that TIPS’ interest rates are protected against changes in the inflation rate. So I had assumed that we can deduce the bond market’s expectations of future inflation by comparing their yields.

… My argument appeared to make perfect sense, and I certainly was not the only one that was making it. But I now believe that I was wrong. Interpreted correctly, the message of the bond market actually is that inflation is indeed going up.

… My education came courtesy of Stephen Cecchetti, a former director of research at the New York Fed and currently professor of global finance at Brandeis University. In an interview, Cecchetti pointed out that other factors must be introduced into the equation when deducing the market’s inflationary expectations from the spread between the yields on TIPS and regular Treasuries.

The most important of these other factors right now is the relative size of the markets for TIPS and regular Treasury securities. Whereas the market for the latter is huge — larger, in fact, than the equity market — the TIPS market is several orders of magnitude smaller. This means that, relative to regular Treasuries, TIPS yields must be higher to compensate investors for this relative illiquidity.

And that, in turn, means that the spread between the yields on regular Treasuries and TIPS will understate the bond market’s expectations of future inflation.

Complicating factors even more is that this so-called illiquidity premium is not constant. So economists have had to devise elaborate econometric models to adjust for it and other factors. And those models are showing inflationary expectations to have dramatically worsened in recent months.

I have never met Mr. Hulbert, nor read any of his other articles.  I cannot claim that I wouldn’t have made the same mistake and I have to tip my hat to him for being willing to face up to it.  There are remarkably few people who would do that.