Paper Trail #8: Common Risk Factors in the Returns on Stocks and Bonds (Fama & French, 1993)
In February 1993, Eugene Fama and Kenneth French published Common risk factors in the returns on stocks and bonds in the Journal of Financial Economics. The paper is the methodological source of every “factor investing” ETF on the market today. Its central empirical finding: adding two factors (SMB and HML) to the market excess return takes the variance-explained on 25 size-BE/ME test portfolios from CAPM’s 2 of 25 above R² 0.9 to the three-factor model’s 21 of 25 above R² 0.9.
Citation: Fama, Eugene F. and Kenneth R. French, “Common risk factors in the returns on stocks and bonds”, Journal of Financial Economics 33 (1993), pages 3-56. Received July 1992, final version September 1992. Both authors at the University of Chicago. Full 54-page PDF verified via WebFetch of the University of Houston Bauer College mirror at bauer.uh.edu/rsusmel/phd/Fama-French_JFE93.pdf on 2026-08-08 — every quantitative claim in this post traces to a specific passage in that PDF.
The problem the paper solves
By the late 1980s, empirical work had turned up a growing list of stock-return anomalies that CAPM couldn’t explain. Small firms earned higher returns than their market betas predicted (Banz 1981, cited in the paper’s introduction). High book-to-market firms earned higher returns than their market betas predicted (Rosenberg, Reid, and Lanstein 1985 among others, also cited). Firms with high earnings-to-price ratios did too (Basu 1983). Fama and French’s own 1992 paper (widely known as “the beta is dead” paper in trading circles) had already shown that when size and BE/ME were both included in a cross-sectional regression, market beta added no explanatory power for average returns.
The 1993 paper does two things: it moves from a cross-sectional regression framework to a time-series regression framework (which makes the factor structure explicit and lets you compute R² per portfolio), and it introduces the specific SMB and HML factor construction that has become the industry standard.
SMB and HML: the construction
Each June, sort NYSE-listed stocks on two dimensions:
Size (ME).Market capitalisation = price × shares outstanding, measured at the end of June. Split at the NYSE median: everything at or below is “small” (S); everything above is “big” (B).
Book-to-market equity (BE/ME).Book value of common equity from Compustat divided by market cap. Split at the 30th, 70th percentiles: bottom 30% is “low” (L, the growth stocks); middle 40% is “medium” (M); top 30% is “high” (H, the value stocks).
The intersection produces six portfolios: S/L, S/M, S/H, B/L, B/M, B/H. These are rebalanced annually in June and held for twelve months. The two factor portfolios are then:
SMB = (S/L + S/M + S/H)/3 − (B/L + B/M + B/H)/3 HML = (S/H + B/H)/2 − (S/L + B/L)/2
By construction, SMB is long-small / short-big while averaging over BE/ME (so the size signal isn’t mixed with a value signal). HML is long-high-BE/ME / short-low-BE/ME while averaging over size (so the value signal isn’t mixed with a size signal). Both are zero-net-investment long-short portfolios that can be treated as pure risk factors.
The factor premia in the paper’s sample
Over July 1963 to December 1991 (342 months of monthly data), the paper reports these averages:
| Factor | Mean (% / month) | t-stat | Approx annualised |
|---|---|---|---|
| RM−RF (market) | +0.43% | — | +5.2% |
| SMB (size) | +0.27% | 1.73 | +3.2% |
| HML (value) | +0.40% | 2.91 | +4.8% |
HML clears statistical significance at the standard 5% threshold (t = 2.91, p ≈ 0.004 at 341 dof); SMB does not (t = 1.73, p ≈ 0.084). Fama and French describe HML’s 0.40% per month as “an average premium of 0.40% per month (t = 2.91), that is large in both practical and statistical senses.”
The 25-portfolio test
The paper’s core diagnostic is to run time-series regressions of 25 test portfolios (a 5×5 sort on size and BE/ME — finer than the 6 portfolios used to construct the factors) on the factor returns. If the factor model fits the data, the regression intercepts should be near zero and the R² should be high.
CAPM (RM−RF only) R² > 0.9 for 2 of 25 portfolios Three-factor (+SMB +HML) R² > 0.9 for 21 of 25 portfolios
Verbatim from the paper: “in the three-factor regressions (table 6) R² values greater than 0.9 are routine (21 of 25). Even the lowest three-factor R² for stocks, 0.83 for the portfolio in the largest-size and highest-BE/ME quintiles, is much larger than the 0.69 [obtained under CAPM]”. Only 3 of 25 three-factor intercepts differ from zero by more than 0.2% per month; 16 are within 0.144% of zero. In plain English: the three factors together explain almost all of the average-return differences across the 25 test portfolios.
The bond factors: TERM and DEF
The paper’s second contribution — often forgotten in the stock-focused retelling — is a two-factor model for bond returns:
TERM = long-term government bond return minus one-month T-bill return. Proxy for the slope-of-yield-curve risk factor — how much you get compensated for holding duration.
DEF = long-term corporate bond return minus long-term government bond return. Proxy for default-risk compensation — the credit spread realised over the sample.
The paper then shows that TERM and DEF are large-R² drivers of bond returns, and that stock returns also load meaningfully on TERM and DEF (though less than they load on RM-RF, SMB, HML) — the five factors together are the “common risk factors in the returns on stocks and bonds” of the title.
Where this connects to earlier Paper Trail posts
Paper Trail #4 (Fama 1970, efficient markets). Same first author. Fama 1970 argued CAPM was the appropriate equilibrium framework for interpreting “expected returns”. Fama-French 1993 shows CAPM doesn’t adequately describe the cross-section of returns on real data and offers a three-factor alternative. This is Fama updating his own priors 23 years later based on the empirical work. Fama-French 1993 does NOT retract the efficient-markets framing of Fama 1970 — SMB and HML can still be interpreted as compensating for genuine (previously-unrecognised) risks, in which case the market is efficient with respect to a richer information set than pure CAPM assumed.
Paper Trail #7 (Barber & Odean 2000, trading is hazardous to your wealth).When Barber and Odean computed risk-adjusted household returns, the FF 3-factor model was one of THE benchmark models they used. That’s the direct connection the content ledger flagged when queueing this installment. If you want to say “this trader beat the market” in a way that isn’t a re-labelling of size-and-value tilt, you have to net out FF 3-factor exposure first — Barber & Odean 2000 does exactly this, and finds that even after that adjustment, high-turnover households underperform.
Paper Trail #2 (Jegadeesh & Titman 1993, momentum). Published the same year in the same field. Momentum was NOT one of Fama-French’s three factors — a gap Carhart (1997) subsequently closed with a fourth factor (MOM), and which Fama-French themselves added to their 5-factor 2015 update. This is a live area of empirical work more than three decades after the original paper.
What retail traders should take from this
Every “factor” ETF is implementing this paper.Vanguard, iShares, AQR, and the whole factor-investing subfield build their long-short overlays using SMB and HML construction rules that trace directly back to the recipe in this paper. When a factor ETF advertises “value tilt” it’s tilting its holdings toward high-BE/ME stocks in exactly the way the H portfolios of the paper’s original construction did.
Benchmark selection matters.If you’re evaluating a discretionary or systematic strategy, the risk-adjusted return you compute depends critically on what risks you’re adjusting for. Beating S&P 500 beta by 5% per year while quietly loading on small-cap value can look like alpha but is really factor exposure that would show up as near-zero when regressed on RM-RF + SMB + HML. This applies as much to a discretionary retail portfolio as to a hedge fund.
In-sample premia don’t promise out-of-sample payoff.HML earned 4.8%/year annualised over 1963-1991. In the subsequent 30+ years the premium has been meaningfully smaller, and value strategies underperformed growth for extended stretches (2010-2020 famously). This isn’t the model being wrong — a factor with a positive expected premium can still deliver a negative realised premium over a decade or two — but it is a caution against treating the in-sample numbers as forward-looking forecasts. That’s the same caveat Stats for Traders #3 made about small-sample confidence intervals on FX bucket medians, extended to a different asset class.
The paper is one of the most-cited in modern empirical finance (roughly 40,000 citations by 2025 on Google Scholar). It won the Sharpe-Award for that year’s best JFE paper. Fama was awarded the Nobel in 2013 with Hansen and Shiller for empirical asset pricing — this paper was part of the citation. The three-factor model is the standard benchmark that any factor research today is expected to at minimum reproduce and improve upon.
Paper on ScienceDirect (JFE) — Full PDF (University of Houston Bauer College mirror).