Quick Answer
EMH holds that prices already reflect available information, so consistently beating the market through stock picking or timing is not possible. The weak, semi-strong, and strong forms differ only in how much information is assumed priced in, which determines whether technical analysis, fundamental analysis, or even insider information can still add value.
This section walks through each form's assumptions, distinguishes weak from semi-strong from strong, and closes with what EMH implies for active versus passive management.
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.
What Are the 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 |
What Does the Weak Form Say?
- 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
What Does the Semi-Strong Form Say?
- 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
What Does the Strong Form Say?
- 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 form to pin down. 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.
What Does EMH Imply 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.
What Should You Check on Exam Day?
- Weak form: technical analysis is useless; fundamental analysis may still add value.
- Semi-strong form (the form to pin down): neither technical nor fundamental analysis can consistently beat the market; only insider information could still provide an edge.
- Strong form: no one, not even insiders, can consistently earn excess returns.
- Insider trading regulations are evidence against the strong form, since insiders do have an information advantage.
- EMH supports passive management and index funds; active management assumes markets are not fully efficient.