9.3 Efficient Market Hypothesis

The Efficient Market Hypothesis, developed by Eugene Fama in 1970, is one of the most debated theories in finance. It argues that asset prices fully reflect all available information, making it impossible to consistently "beat the market."

Core Concept

In an efficient market:

- Prices adjust rapidly and accurately to new information

- Securities are fairly priced at all times

- No investor can consistently earn risk-adjusted excess returns

- Active management cannot systematically outperform passive strategies

The Three Forms of EMH

Each form makes progressively stronger claims about what information is reflected in prices:

Weak Form Efficiency

Claim: Prices reflect all historical market data (past prices, volume, trading patterns).

- What's Reflected: Past prices; Analysis That Won't Work: Technical analysis; Analysis That Might Work: Fundamental analysis

- What's Reflected: Historical volume; Analysis That Won't Work: Chart patterns; Analysis That Might Work: Insider information

- What's Reflected: Previous returns; Analysis That Won't Work: Momentum strategies

Implication: Technical analysis is useless. You cannot predict future prices by studying past prices.

Semi-Strong Form Efficiency

Claim: Prices reflect all publicly available information (financial statements, news, economic data).

- What's Reflected: All public information; Analysis That Won't Work: Technical analysis; Analysis That Might Work: Insider information

- What's Reflected: Financial statements; Analysis That Won't Work: Fundamental analysis

- What's Reflected: Economic data; Analysis That Won't Work: News-based trading

- What's Reflected: Analyst reports

Implication: Neither technical NOR fundamental analysis can produce excess returns. By the time you read a financial statement or news article, the price has already adjusted.

Strong Form Efficiency

Claim: Prices reflect ALL information, including private (insider) information.

- What's Reflected: All public information; Analysis That Won't Work: Technical analysis

- What's Reflected: All private information; Analysis That Won't Work: Fundamental analysis

- What's Reflected: Insider knowledge; Analysis That Won't Work: Insider trading

Implication: Even insiders cannot profit from their information. This form is generally NOT supported by evidence - insider trading prosecutions prove that private information has value.

Summary of EMH Forms

- Weak: Information Reflected: Past prices/volume; Technical Analysis: Useless; Fundamental Analysis: May work; Insider Trading: May work

- Semi-Strong: Information Reflected: All public info; Technical Analysis: Useless; Fundamental Analysis: Useless; Insider Trading: May work

- Strong: Information Reflected: All info (public + private); Technical Analysis: Useless; Fundamental Analysis: Useless; Insider Trading: Useless

Evidence For and Against EMH

Evidence Supporting EMH

Active Manager Performance:

- Over 15 years, 88% of large-cap active managers underperform the S&P 500

- Only about 29% of active funds beat their benchmark over a decade

- Outperformance is rarely persistent - this year's winners are often next year's losers

Market Reactions:

- Stock prices adjust within minutes to earnings announcements

- Merger arbitrage opportunities disappear almost instantly

- Index inclusion effects occur immediately upon announcement

Challenges to EMH (Market Anomalies)

- January Effect: Small stocks outperform in January; Challenge: Predictable pattern should not exist

- Momentum: Recent winners continue winning short-term; Challenge: Past returns shouldn't predict future

- Value Premium: Low P/B stocks outperform long-term; Challenge: Publicly available info shouldn't provide edge

- Small-Cap Effect: Small stocks outperform large (historically); Challenge: Size is public information

- Market Bubbles: Prices deviate dramatically from fundamentals; Challenge: Prices should reflect fair value

Behavioral Finance Critique

Behavioral finance argues that:

- Investors are not always rational

- Cognitive biases lead to systematic errors

- Markets can remain irrational longer than you can remain solvent

- Examples: Overconfidence, herding, loss aversion, anchoring

Investment Implications

If You Believe Markets ARE Efficient:

- Passive indexing: Can't beat the market, so match it

- Minimize costs: Fees reduce returns without adding value

- Focus on asset allocation: Primary driver of long-term returns

- Tax efficiency: One area you can control

- Broad diversification: Don't try to pick winners

If You Believe Markets Are INEFFICIENT:

- Active management: Skilled managers can exploit mispricings

- Research and analysis: Information analysis can add value

- Concentrated positions: High-conviction ideas can outperform

- Factor investing: Exploit known anomalies

The Practical View

Most investment professionals take a middle ground:

- Markets are mostly efficient, most of the time

- Some inefficiencies exist, especially in less-followed markets

- Active management can add value, but it's difficult and costly

- A combination of passive (core) and active (satellite) may be optimal

On the Exam

Series 65 frequently tests:

- Identifying which form of EMH is described in a scenario

- Understanding what analysis is useful under each form

- Recognizing investment implications of market efficiency

- Knowing that strong form is NOT supported by evidence

Key Takeaways

1. EMH claims prices reflect available information

2. Weak form: Past prices reflected - technical analysis useless

3. Semi-strong: All public info reflected - fundamental analysis useless

4. Strong form: All info reflected - NOT supported by evidence

5. Most active managers underperform their benchmarks

6. If markets are efficient, passive indexing is the logical choice