Paper Trail #2: Momentum (Jegadeesh & Titman, 1993)
Sorting US stocks into deciles by their return over the previous 12 months, then buying the top decile and shorting the bottom decile for the next 3 months, produced 1.31% per month of return over 1965–1989. Skip a week between the ranking and the holding period and it rises to 1.49% per month, with a t-statistic of 4.28. That’s the finding that turned “buy what’s going up” from folk wisdom into a documented anomaly.
This is Paper Trail #2. Same rules as last time: every claim comes from the paper itself, not a summary of it, and every number traces back to a table I read.
The paper
Jegadeesh, N., & Titman, S. (1993). “Returns to Buying Winners and Selling Losers: Implications for Stock Market Efficiency.” The Journal of Finance, 48(1), 65–91. JSTOR stable ID 2328882.
The paper opens with a puzzle: the then-recent literature (De Bondt & Thaler 1985, Jegadeesh 1990, Lehmann 1990) had found strong evidence for contrarian strategies — buying past losers, selling past winners — at both very short (weekly) and very long (3–5 year) horizons. But practitioner strategies like Value Line rankings and many active mutual funds were doing the opposite: buying past winners on a 3–12 month horizon. The paper systematically tests that middle horizon.
The strategy, precisely
Every month, rank all NYSE + AMEX stocks by their return over the past Jmonths (with J = 3, 6, 9, or 12). Form ten equal-weight decile portfolios. Long the top decile (“winners”), short the bottom decile (“losers”). Hold the position for K months (with K = 3, 6, 9, or 12). This produces 4 × 4 = 16 strategies. The paper tests all 16, plus another 16 variants that skip a week between the ranking and the holding period to sidestep bid-ask bounce and short-term reversal effects.
Data: CRSP daily returns file, sample period January 1965 to December 1989 (300 months).
The result
| Formation J | K=3 | K=6 | K=9 | K=12 |
|---|---|---|---|---|
| 3 months | 0.32% | 0.58% | 0.61% | 0.69% |
| 6 months | 0.84% | 0.95% | 1.02% | 0.86% |
| 9 months | 1.09% | 1.21% | 1.05% | 0.82% |
| 12 months | 1.31% | 1.14% | 0.93% | 0.68% |
The table above is Panel A of the paper’s Table I (page 70): the average monthly return of the winners-minus-losers zero-cost portfolio in percent per month, no lag between formation and holding. Every cell is positive. All are statistically significant except the 3-month/3-month strategy. The maximum is the highlighted cell: J=12, K=3, 1.31% per month. With a 1-week lag between formation and holding (Panel B in the paper), that same cell rises to 1.49% per month with a t-statistic of 4.28.
The paper spends Sections III–V ruling out the two obvious risk-based explanations: the profits aren’t due to systematic beta (in fact the winners-minus-losers portfolio has a slightly negative beta of -0.08in Table II), and they aren’t explained by a lead-lag between big and small stocks. That’s the finding that made the paper important: the returns exist and don’t line up with the standard risk factors, so they’re either compensation for a risk the standard models don’t capture, or evidence of a market inefficiency.
The catch: it reverses
Section VI of the paper — the one anyone quoting the abstract tends to skim — traces the 6-month/6-month strategy’s stocks beyond the 6-month holding window. The result:
- Cumulative return over the first 12 months post-formation: +9.5%.
- The strategy then gives back more than half of that return over the following 24 months.
- The reversal starts around month 12 and continues through month 31.
In plain English: momentum stocks keep going up for about a year, then materially underperform for the next two. The 3–12 month edge is real; extending the holding period to catch “more of the move” is exactly what unwinds it.
What this doesn’t say (my extrapolation)
The paper is a study of equal-weighted decile portfolios of US stocks on the NYSE and AMEX over 1965–1989. A retail trader reading it should not extrapolate freely. Three specific limits:
It doesn’t say “buy currencies that are going up.”The 1993 paper is stocks only. A separate literature (Menkhoff, Sarno, Schmeling & Schrimpf, 2012, Journal of Financial Economics) tests currency momentum and finds a smaller, riskier version of the effect. Applying the 1.31%/month number to FX is a category error.
It doesn’t say a single winning stock will keep going up. The profits are the average of a ten-percent-tail portfoliominus a ten-percent-tail portfolio, held for months, rebalanced monthly with overlapping holding windows. That’s a different object from a buy-and-hold trade in one instrument.
It doesn’t say the effect will persist in out-of-sample data.The paper’s Section VII back-tests the strategy over 1927–1964 and finds it also worked there — so the effect isn’t period-specific to 1965–1989. But subsequent literature (surveyed for example by Israel & Moskowitz, 2013, “The Role of Shorting, Firm Size, and Time on Market Anomalies”, Journal of Financial Economics 108(2)) has continued to debate whether momentum profits are as strong in post-publication data as they were in the 1965–1989 sample. Any strategy sourced from a 1993 finding needs its own out-of-sample check on recent data before it’s put to work.
Why it’s useful anyway
The most-cited retail takeaway from Jegadeesh & Titman is that past return contains information about future return over a 3–12 month horizon — enough to matter and not obviously arbitraged away by the time this paper published. That’s a serious finding even if the specific magnitudes don’t generalize to individual instruments or to today’s market. It’s also the finding that pushed the field to include a “momentum” factor alongside size and value in the multi-factor asset-pricing models that came after — Carhart’s four-factor model (1997) added it explicitly, and it’s been a fixture of the literature ever since.
The second-most-cited takeaway, less popular in retail discussions, is Section VI’s reversal. If you take momentum seriously as an edge, you also have to take seriously that holding-period matters, and that stretching for more of a move by holding longer is exactly the way the effect goes away.