Saturday, 7 January 2012
Efficient Market Hypothesis: Fact Or Fiction?
Our economics series looks at the question of whether we really can beat the market.
How many times have you heard a would-be private investor saying something like: "You can't beat the game, because the big institutions always get the information ahead of you and get in first"?
If you believe that, you might be a proponent of the Efficient Market Hypothesis, which says that because the financial world is efficient in terms of information, it is impossible to consistently beat the market based on what you know when you choose where to put your money.
The idea was first developed by the economist Eugene Fama in the 1960s, following on from his observations that the day-to-day movements of the stock market resemble a random walk as much as anything else. And for a while, it came to be pretty much accepted as fact.
On the face of it, it does seem reasonable. Given that everyone has access to the same information, and there is a truly free price-setting equilibrium in which the balance of supply and demand is the determining factor in setting share prices (as it pretty much is with any free-traded commodity), surely the price will reflect all of the information available at the time, and you can't beat the market.
In the short term, the idea seems pretty much spot-on. New results are released and they look good, and you try to get in 'ahead of the market' to profit from them? Well, no matter how quick you are, it's too late and the price has already jumped. That's really no surprise, because the sellers of the shares have the same new information too, and the equilibrium point between supply and demand will instantly change.
But in the longer term, the Efficient Market Hypothesis is widely considered to be flawed. In fact, if you believed it held true over serious investing timescales, you probably wouldn't be reading this -- you'd have all your investing cash in a tracker fund and you'd be spending your spare time doing something else. (And that's actually not a bad idea at all, but it's perhaps something for another day).
There is plenty of empirical evidence that the market is what Paul Samuelson described as "micro-efficient" but "macro-inefficient", such that it holds true for individual prices over the short term but fails to explain longer-term whole-market movements.
And there are others, including the noted contrarian investor David Dreman, who argue that this "micro efficiency" is no efficiency at all, claiming instead that short-term response to news is not what investors should be interested in, but the longer-term picture for a company. It's pretty clear which side of that argument Foolish investors will come down on.
So why doesn't it work in the long run, and how is it possible to beat the market even in the presence of the ubiquity of news and an instantly adjusting price mechanism? Well, the major flaw is that the theory assumes that all participants in the market will act rationally, and that the price of a share will always reflect a truly objective assessment of its real value. Or at least that the balance of opinion at any one time will even out to provide an aggregate rational valuation.
It doesn't take a trained economist to realise what nonsense that can be. Any armchair observer who watched supposedly rational investors push internet shares up to insane valuations during the tech share boom around the year 2000 saw just how the madness of crowds can easily overcome calm rationality.
And the same is true of the recent credit crunch, when panicking investors climbed aboard the 'sell, sell, sell' bandwagon, pushing prices for many a good company down to seriously undervalued levels. What happens is that human emotion just about always outstrips rationality -- good things are seen as much better than they really are, and bad things much worse.
And it's not just these periods of insanity, either. There is, for example, strong evidence that shares with a low price-to-earnings ratio, low price-to-cash-flow ratio and so on, tend to outperform the market in the long run. And high-expectation growth shares are regularly afforded irrationally high valuations, and end up reverting to the norm and failing to outperform in the long term.
So what does that all say about the Efficient Market Hypothesis? Well, it certainly contributes to understanding how markets work, but we also need to include emotion, cognitive bias, short-term horizons and all sorts of other human failings in the overall equation.
And that means we can beat the market average in the long term, if we stick to objective valuation measures, don't let short-term excitements and panics sway us, and rein in our usual human over-optimism and over-pessimism.