Debunking the Myth of Market Efficiency


Sixty years after it was first formulated, the core tenet of the efficient market hypothesis (EMH) — that stock prices fully reflect all available information — continues to be considered gospel truth in lots of quarters: Investors can only expect to earn a standard rate of return because prices adjust before investors can trade on fresh information.

Hypothesizing about Markets

One other key postulate of the EMH is investor rationality. That’s, investors will routinely adjust their valuation estimates to each latest piece of data. The EMH acknowledges that individuals can independently deviate from rational behavior. But a 3rd assumption of the speculation is that irrationally optimistic investors are only as common as irrationally pessimistic ones and thus “prices would likely rise in a way consistent with market efficiency,” because the authors of Corporate Finance explain.

While arguing that such irrationality is invariably offset could appear just a little too tidy and unrealistic, a fourth EMH assumption holds that irrational amateurs will face rational and intuitive professionals who will make the most of any temporary mispricing through arbitrage.

A fifth fundamental inference is that of perfect competition. No investor can control any segment of the market and extract monopoly profits for lengthy periods.

As a consequence of the above, there aren’t any patterns in share price changes and costs in any respect times express true value. Prices follow a random walk, and no investor can consistently earn cash from trend-following, momentum-buying, or every other investment style.

To anyone with experience in the general public markets, these axioms — perfect information, investor rationality, an irrationality-offsetting mechanism, systematic arbitrage, and excellent competition — are, at best, farfetched. But as sociologist Raymond Boudon observed, “people often have good reason to consider in dubious or false ideas,” which could be reinforced by flawless arguments based on conjectures. One particular belief Boudon flagged is that of homo economicus as a rational being, “almost God’s equal.”

What makes the EMH so appealing is the premise that markets are optimal capital allocators and wealth creators. That capitalism trumps planned economies doesn’t validate the speculation, nevertheless. Here, Max Weber’s core research principle applies: “Statements of fact are one thing, statements of value one other, and any confusing of the 2 is impermissible.” That is where the EMH erred.

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Deconstructing Market Efficiency

Let’s review why the EMH’s economic interpretation is questionable.

1. Information Accuracy

To begin with, the notion of perfect information ignores the undeniable fact that information could be manipulated, inaccurate, misleading, fraudulent, or just difficult or not possible to grasp.

Rigging markets shouldn’t be a latest technique. Creative accounting and outright fraud are common, particularly during bubbles and market corrections. The dot-com and telecom manias led to varied scandals. The newest euphoria orchestrated by central banks’ zero interest-rate policies brought on Wirecard and FTX, amongst other excesses.

In the times of faux news and quick messaging, the claim that market prices contain all available data fails to consider the danger of misrepresentation.

2. Information Access

Market prices can only reflect perfect information if all investors access the identical data at the identical time. In the UK, as an example, a fifth of public takeovers are preceded by suspicious share price movements. Insider trading is rife and has all the time been.

In an April 1985 study of all takeovers, mergers, and leveraged buyouts from the yr before, BusinessWeek magazine found that the stock price rose in 72% of the cases before the transaction was publicly announced. As Drexel CEO Fred Joseph put it: “the arbs [arbitrageurs] have perfected the strategy of obtaining inside information.”

Disparate data access doesn’t solely affect stock and bond exchanges. 4 years ago, the Bank of England and US Federal Reserve discovered that some traders and hedge funds received policymakers’ statements as much as 10 seconds before they were broadcast.

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3. Information Processing

Sophisticated investors analyze information in a methodical, rigorous, and speedy way. Algorithmic tools give institutions an unassailable edge against less experienced investors.

The success of quantitative trading at Jim Simons’s Renaissance Technologies and other hedge funds demonstrates that superior data evaluation may help beat the market consistently, even when not on a regular basis.

Mass investor confusion is an actual phenomenon. Investors mistook the Chinese company Zoom Technologies with the newly listed Zoom Video in 2019, sending the previous’s stock soaring 70000%. A yr later, because the world went into lockdown, it happened again. These are isolated anecdotes to be certain, but given such basic mistakes, is it credible to posit that stock prices accurately reflect all available information?

Beyond Information

A significant shortcoming of the EMH is that it offers a narrow definition of market efficiency, focusing wholly on data availability. This oversimplification fails to acknowledge that the market is greater than just a mirrored image of knowledge flows. Other aspects can create friction.

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1. Trade Execution

Once investors access, process, and analyze information, they need to have the opportunity to execute trades seamlessly. Market makers and skilled traders can have this ability, but individual investors don’t. The front-running scandal at Robinhood, when customer order data was shared with high-frequency traders (HFTs), is only one example of the uneven playing field.

This type of practice is nothing latest. In The Man Who Solved the Market, Gregory Zuckerman explains how within the mid-Nineteen Nineties, “shady traders were taking advantage” of Simons’s exertions by “watching [his fund] Medallion’s trades.” Michael Lewis described how HFTs speed up trade execution in Flash Boys. They deploy computer-driven trading robots, access private venues called “dark pools” to cover transactions, move physically closer to public exchanges to trade ahead of other participants, and pay intermediaries for early access to information — all to artfully maintain an unfair advantage.

Superfast connections and algorithmic trading should democratize access to stock exchanges, improve liquidity, and lower spreads not rig markets by enabling front-running.

2. Price Setting

In keeping with the EMH, price changes are statistically independent from each other. They occur as latest data emerges; there aren’t any trends for investors to discover. The market’s response to latest data includes no investor overreaction or delay. Prices all the time reflect all available information.

Benoit Mandelbrot’s pre-EMH research demonstrated that stock prices were characterised by concentration and long-range dependence. Recent information moved markets, but so did momentum and other aspects unrelated to data flows. Investors could earn cash from trend-following, momentum, seasonality, and other strategies. This contradicts the EMH, and further research into persistent return anomalies supports the conclusion.

As Warren Buffett observed in his coin-flipping article about superinvestors in Graham-and-Doddsville, it is feasible to consistently beat the market.

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3. Investor Behavior

Investor rationality possibly the weakest of the EMH’s assumptions.

Behavioral economists have long maintained that investors are emotional. Robert Shiller demonstrated that stock prices are more volatile than could be expected if investors were strictly rational. Investors are inclined to overreact to unexpected news.

That the actions of irrational investors are someway neutralized by arbitrageurs, or by other irrational investors taking opposite positions, has all the time gave the look of wishful considering. That the price-setting process is devoid of speculation is equally unsound as theory. If speculation may explain price movements in cryptocurrency markets or for meme stocks, with no underlying money flows or corroborative performance data, why couldn’t it play a task in broader market activity?

Verification and Falsification

Behaviorists and EMH advocates fiercely debate market efficiency. Eugene Fama, one in every of the EMH’s pioneers, has acknowledged that the speculation can’t be fully tested. “It’s not completely true,” he said. “No models are completely true.” Partly for that reason, he defined three kinds of efficiency: a weak form, based on historical trends; a semi-strong form, which incorporates all public information; and a powerful form whose price trends also include private information.

The strong form has long been discredited, if only attributable to rampant insider trading and instances of market manipulation by sophisticated investors to the detriment of less experienced punters — witness recent excesses with SPAC structures.

The semi-strong form never looked credible either given Mandelbrot’s research and Buffett’s superinvestors. Market prices don’t solely rely on information.

Investor rationality is the core assumption behind many economic theories, but philosopher Karl Popper explained that such “theories . . . are never empirically verifiable.” They can not be considered true until proven in a universal and unconditional manner, yet they could be falsified at any moment.

For Popper, probably the most uncertain theories tend, by necessity, to be probably the most resistant to criticism. The iterative strategy of falsification and verification is limitless and results in intermediate conclusions. The issue is knowing when enough contradictions have accrued to desert a theory.

Multiple Truths

Financial markets are faulty, but just how faulty shouldn’t be clear. Unless and until it’s incontrovertibly falsified, the EMH will proceed to prevail. Recognizing its detractors’ weak standing, Fama stated that “there is no such thing as a behavioral asset pricing model that could be tested front to back.” The identical is true, after all, of his own market efficiency model.

Markets are at times efficient, at other times inefficient. They might even be each concurrently. That is what proponents of a hybrid version seek to find out. Andrew Lo’s theory of adaptive markets, as an example, blends facets of each market efficiency and behaviorism.

In the event that they are neither solely informational nor fully behavioral, markets are also unlikely to be each exclusively. Their complexity transcends disciplines and can’t be entirely modeled out. But this doesn’t contravene the concept that it is feasible to beat the market repeatedly through sheer luck — in a type of coin-flipping contest, with skills and experience — using algorithmic or alternative methods, or through inside information and other criminal means.

Even though it appears purely random, there’s order inside the chaos of economic markets. The predominant challenge for investors stays how one can devise an investment style that consistently, even when not always, outperforms.

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All posts are the opinion of the writer. As such, they shouldn’t be construed as investment advice, nor do the opinions expressed necessarily reflect the views of CFA Institute or the writer’s employer.

Image credit: ©Getty Images / AmandaLewis

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