The research question
Momentum appears in multiple markets and geographies, but the gross premium is not the same thing as a readily tradable retail return. The literature also documents concentrated crash episodes after sharp market reversals.
The useful question is not whether a chart once went up. It is whether the hypothesis has a clear economic mechanism, appears outside one hand-picked sample, can be reconstructed with information that was available at the time, and remains plausible after realistic implementation frictions.
Minimum viable rule
Rank prior returns, commonly from month 12 through month 2, then compare a winner portfolio with a loser portfolio.
Universe: Large, liquid equities with survivorship-aware data. A credible test fixes the universe, timestamps, missing-data policy and rebalance convention before model selection. Results should be shown both gross and net of an explicit cost model.
Implementation audit
Universe definition, delisting returns, point-in-time constituents, skip-month convention, turnover and borrow assumptions are central. A long-only tilt is operationally different from the academic long-short factor.
At minimum, an audit should report turnover, worst peak-to-trough loss, recovery time, exposure concentration and sensitivity to neighboring parameter choices. A strategy that works only at one exact lookback or threshold deserves a lower level of confidence.
How the idea can fail
Momentum can suffer abrupt losses when beaten-down assets rebound. Crowding, turnover, taxes, bid-ask spreads and short availability can consume a large share of the historical premium.
Failure conditions belong in the strategy definition. They provide a disciplined reason to investigate or stop, instead of changing the story after a loss.
Primary source
Value and Momentum Everywhere
Asness, Moskowitz & Pedersen (2013), Journal of Finance 68(3), 929–985.
DOI record
This page is an independent educational synthesis. It does not reproduce the paper and does not claim that published historical results are currently achievable.