The Efficient Market Hypothesis (EMH) states that security prices fully reflect all available information. EMH implies that consistently beating the market through stock picking or market timing is not possible. The Series 65 exam tests the three forms of EMH and their implications for investment strategy.
Three Forms of EMH
Each form has a different definition of "available information":
| Form | Information Reflected in Prices | Technical Analysis | Fundamental Analysis | Insider Info |
|---|---|---|---|---|
| Weak | All past market/trading data (prices, volume) | Useless | May still work | May still work |
| Semi-strong | All public information (financial statements, news, filings) | Useless | Useless | May still work |
| Strong | All information (public AND private/insider) | Useless | Useless | Useless |
Weak Form
- Prices reflect all historical trading data (past prices, volume)
- Technical analysis (charts, patterns) is useless
- Fundamental analysis may still add value (public info not yet in prices)
- Past prices contain no information not already reflected in the current price
Semi-Strong Form
- Prices reflect all publicly available information (includes weak form + financial reports, news, analyst reports)
- Neither technical nor fundamental analysis can consistently beat the market
- Only insider information could provide an edge (but trading on it is illegal)
- Most widely accepted form among academics
Strong Form
- Prices reflect ALL information, including insider/private information
- No one, not even insiders, can consistently earn excess returns
- Generally considered too extreme and not fully supported
- The existence of insider trading regulations is evidence against the strong form (insiders DO have an information advantage)
Each form builds on the previous one: Weak includes historical data; semi-strong adds all public information; strong adds private/insider information.
Think of it this way: Imagine thousands of smart investors all analyzing the same stocks. As soon as any piece of information becomes available, they all act on it immediately. Stock prices quickly adjust to reflect all known information. By the time you hear about something, it is already priced in. That is why EMH says you cannot consistently "beat the market."
Exam Tip: Gotchas
- The semi-strong form is the most commonly tested. The exam tests whether you know that semi-strong EMH means fundamental analysis cannot beat the market. A common trap: if a question describes an investor who reads financial statements to find undervalued stocks, that strategy only works if markets are NOT semi-strong efficient.
- The existence of insider trading regulations is evidence AGAINST the strong form. Insider trading laws exist precisely because insiders DO have an information advantage.
EMH Implications for Investment Strategy
- If markets are efficient, active management (stock picking, market timing) cannot consistently outperform
- Supports passive management (index funds) as the optimal strategy
- Index funds have lower fees and match market returns, consistent with EMH
- EMH does NOT mean prices are always correct; it means prices reflect available information and mispricings are quickly corrected
| Market Efficiency | Recommended Strategy | Rationale |
|---|---|---|
| Weak form | Fundamental analysis, passive | Technical analysis adds no value |
| Semi-strong form | Passive (index funds) | Neither technical nor fundamental adds value |
| Strong form | Passive (index funds) | No strategy adds value |
Think of it this way: If markets are semi-strong efficient, paying high fees to active managers is a waste because they cannot consistently outperform. This is the theoretical foundation for the rise of passive index investing.
Exam Tip: Gotchas
- EMH supports passive investing and index funds. If a question asks which investment approach is most consistent with the efficient market hypothesis, the answer is passive management / indexing. Active management assumes markets are NOT fully efficient.