Efficient Markets and Factors

Can you beat the market? Investors, fund managers and academics have wrestled with that question for decades. Research gives a more nuanced answer than either camp usually admits – with very practical consequences for how you should invest.

The efficient market hypothesis#

In the 1960s, economist Eugene Fama formulated the efficient market hypothesis (EMH). Its core claim: in an efficient market, prices reflect all available information. New information is priced in so quickly that nobody can profit from it systematically.

Fama distinguished three forms:

The strong form is plainly false – insider trading is illegal precisely because it works. The weak and semi-strong forms are still debated.

Evidence for efficient markets#

• Active funds rarely beat their index: as covered in Module 2, around 85–90% of active stock funds trail their benchmark after costs over 15 years.
• Success rarely persists: funds that are top performers in one period seldom repeat in the next.
• Prices react instantly: earnings and takeover news are priced in within seconds.

The critics: bubbles and anomalies#

Robert Shiller showed that stock prices swing far more than subsequent dividends would justify – a sign of overreaction. Bubbles like the dot-com mania are hard to square with perfectly efficient markets. Then there are anomalies: recurring return patterns that shouldn’t exist in theory.

In 2013, Fama and Shiller – together with Lars Peter Hansen – shared the Nobel Prize for their empirical analysis of asset prices. The message: in the short run prices are barely predictable, but over longer periods there are some patterns – for example, very high valuations tend to mean lower future returns.

Factors: the building blocks of returns#

Since the 1990s, research has examined characteristics associated with higher returns, known as factors.

In 1993 Fama and French built a three-factor model of market, size and value that explains much of the difference in returns between stock portfolios; in 2015 they extended it to five factors, adding profitability and investment.

Risk or mistakes?#

Why should factor premiums exist? Two explanations compete:

1. Risk: value and small companies are often weaker and suffer badly in crises. The higher return would be fair compensation for extra risk – and would persist.
2. Behaviour: investors overreact, extrapolate trends and shun boring stocks. The premium would stem from human error and might fade once enough investors exploit it.

The truth probably lies in between – and differs by factor.

Alpha and beta#

This changes the question of what a fund manager actually delivers:

• Beta is the return from moving with the market – cheaply available through an index fund.
• Factor returns can now also be captured cheaply through factor ETFs (smart beta).
• Alpha is only the part of the return that market and factors can’t explain – genuine skill.

Many active funds that did well owed their success to factor tilts, such as a preference for small or cheap stocks. Persistent alpha after costs is very rare.

What it means for you#

Summary#

Markets are efficient enough that most active investors fail to beat them after costs, but not so perfect that bubbles and anomalies don’t exist. Factors such as value, size, momentum and quality explain much of the variation in returns but swing a lot. Genuine alpha is rare. The index fund isn’t surrender – it’s a choice well grounded in science.