# The Efficient Market Hypothesis: Fama's Foundational Framework

Cite as: Gorak, R. (2026). The Efficient Market Hypothesis: Fama's Foundational Framework. Tradicted. https://www.tradicted.com/research/fama-efficient-1970/
Paper: Eugene F. Fama — *Efficient Capital Markets: A Review of Theory and Empirical Work*
Published in: Journal of Finance (1970)
Original: https://docs.cpuc.ca.gov/PublishedDocs/SupDoc/A1704001/770/193982534.pdf

Key finding: In 89 out of 115 mutual funds studied by Jensen over 1955–1964, net ten-year returns averaged -14.6% below the market line, indicating professional fund managers do not possess information unavailable to the market.

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The efficient market hypothesis (EMH) holds that security prices at any time "fully reflect" all available information. Fama (1970) classified evidence across three test categories in "Efficient Capital Markets": weak form, semi-strong form, and strong form. Serial correlations for daily price changes in 30 Dow Jones stocks averaged only .026. Jensen (1968) studied 115 mutual funds over 1955–1964. 89 fell below their risk-adjusted market benchmark, with net ten-year returns averaging -14.6% below the market line.

## What the Study Found

Fama (1965) found serial correlations for daily DJIA returns averaged .026. A correlation of .06 explains only .36% of variation in the next day's price change. Filter trading rules required commissions of ~.1% per turnaround, wiping out any edge from short-term dependence. Ball and Brown (1968) studied 261 firms over 1946–1966. No more than about 10–15% of annual earnings announcement information had not been anticipated by the announcement month. Jensen found 89 out of 115 mutual funds produced net ten-year returns averaging -14.6% below the market line. Excluding loading charges, 72 out of 115 funds still fell below the line, averaging -8.9%.

## Methodology

The paper reviews empirical studies using serial correlation tests, filter rule tests, event study residual analysis, and risk-adjusted performance evaluation. Datasets span 30 DJIA stocks (~1957–1962), 940 NYSE splits (1927–1959), 261 firms (1946–1966), and 115 mutual funds (1955–1964). Risk was controlled using the Sharpe-Lintner expected return framework and market model beta. Jensen used the S&P 500 as market proxy and measured nominal ten-year returns with continuous compounding.

## Key Statistics

| Metric | Finding | Context |
|---|---|---|
| Average daily serial correlation | .026 | 30 DJIA stocks, ~1957–1962; Fama (1965) |
| Explanatory power at r = .06 | .36% of price change variation | Minimum correlation exceeding 2 standard errors; DJIA daily data |
| Minimum NYSE floor trader commission | ~.1% per turnaround | Clearinghouse fee wiping out small-filter trading profits |
| Splits with post-split dividend increases | 71.5% (672 out of 940) | NYSE splits 1927–1959; FFJR |
| Earnings information anticipated pre-announcement | ~85–90% | Ball and Brown (1968); 261 firms, 1946–1966 |
| Mutual funds below market line (net returns) | 89 out of 115 | Jensen; 115 funds, 1955–1964 |
| Average net deviation from market line | -14.6% | Jensen; ten-year returns including loading charges |
| Mutual funds below market line (ex-loading) | 72 out of 115 | Jensen; ignoring loading charges |
| Average deviation ex-loading charges | -8.9% | Jensen; ten-year returns |
| NYSE specialist sell above last purchase | 83% of all sales | Niederhoffer and Osborne |
| NYSE specialist buy below last sale | 81% of all purchases | Niederhoffer and Osborne |
| Transaction-to-transaction reversals vs. continuations | 2–3 times as likely | Niederhoffer and Osborne; NYSE price changes |

## Why This Matters

EMH became the benchmark against which all active management claims are measured. The three-tier framework — weak, semi-strong, and strong form — remains the standard vocabulary for classifying what information can generate excess returns. The Jensen result established that even professional managers with full research resources cannot systematically exploit publicly available information.

## FAQ

### What does EMH predict about stock price patterns?

Fama (1970) showed daily serial correlations averaged .026 across 30 DJIA stocks over ~1957–1962. Any statistical dependence found was too small to support a profitable system. Commissions of ~.1% per turnaround absorbed all edge from small filter rules.

### How quickly do prices adjust to public announcements?

Ball and Brown (1968) found approximately 85–90% of annual earnings announcement information was reflected in prices before the announcement month, across 261 firms over 1946–1966. FFJR found 940 NYSE split stocks fully adjusted by the end of the split month.

### Do professional fund managers beat a passive strategy?

89 out of 115 mutual funds produced net ten-year returns averaging -14.6% below the market line over 1955–1964. Excluding loading charges, 72 of 115 funds still underperformed, averaging -8.9% below the market line.

### What evidence exists against the strong form of EMH?

NYSE specialists sold above their last purchase on 83% of sales. They bought below their last sale on 81% of purchases (Niederhoffer and Osborne). Scholes found that secondary offerings where corporate insiders were sellers produced the largest negative price adjustments of any seller group.

## Source

Fama, E. F. (1970). Efficient Capital Markets: A Review of Theory and Empirical Work. *The Journal of Finance*, 25(2), 383–417.

[Read the full paper →](https://docs.cpuc.ca.gov/PublishedDocs/SupDoc/A1704001/770/193982534.pdf)