Not an implementation claim. This guide is the translation layer between factor papers and portfolios — the arithmetic that determines how much of a published premium survives, not an endorsement that any particular factor’s residual is worth harvesting.
Definition. A factor is tradable to the extent its paper premium survives five sequential haircuts. Each gate below has a magnitude attached; multiply them through before any published number enters your expectations.
Gate 1: Implementation costs — the turnover haircut
The arithmetic from the turnover guide: annual drag = turnover × per-side cost × 2. Value-family factors (annual turnover ~20–50%) lose tens of bps; momentum-family (100–300%+) can lose several percent — against premia measured in low single digits. The construction detail that decides it: rebalance frequency and bands are choices, and the tradable version of most factors is a deliberately slowed version of the published one.
Gate 2: Capacity — where does the premium live?
Decompose the paper’s sort by size bucket. A premium earned mostly in the bottom size quintile has the capacity of that quintile — often single-digit millions per name of realistic daily trading. The zoo literature’s finding that micro-caps carry a large share of anomalies is, restated, a finding that much of the zoo is capacity-free. Value-weighted, large-cap-only replication is the honest capacity test — and the harsh one.
Gate 3: The short side — half the premium, most of the problems
Published long-short premia often earn disproportionately from the short leg — which is where implementation reality concentrates: borrow fees (routinely 1–10%+ annualized on the crowded shorts every factor selects), recalls and buy-ins at the worst moments, and short-squeeze dynamics that turn the leg’s negative skew structural. The standard translations: long-only tilts capture some premia at a fraction of the paper spread; 130/30-style constructions split the difference. A factor whose premium requires the full short leg is tradable only at institutional shorting infrastructure.
Gate 4: Crowding — the premium’s reflexive component
A published factor is a shared factor: its holders become a correlated bloc whose entries compress the premium and whose exits create the factor’s own crash risk (the quant unwinds of 2007 and the momentum reversals of 2009/2020 are the exhibits). Crowding is hard to measure and impossible to ignore; proxies — valuation spreads of the factor portfolio, short interest on the short leg, factor-flow estimates — belong on the same monitor as the premium itself. Crowding also links gates: it raises effective costs (everyone rebalances together) and shrinks capacity (the trade’s aggregate size is the constraint, not yours).
Gate 5: Decay — the premium’s time derivative
Post-publication decay of a third to a half is the base rate. The tradable expectation is the recent, net premium — which for several famous factors is statistically indistinguishable from zero, per the replication meta-studies. Factors with structural or risk-based mechanism stories decay slower than pure statistical regularities — one of the few places where the mechanism question pays cash.
The worked example
Paper: 6%/yr long-short premium, equal-weighted, monthly rebalanced, 1980–2015. Translation: value-weight and drop micro-caps (−2%), slow to quarterly with bands (turnover 150%→60%, saving 1.1% of a 1.35% cost drag), long-only tilt (capture ~40% of remaining spread), decay haircut (−35%): ≈1.0–1.3%/yr of tradable tilt premium — before crowding risk. Not nothing at scale; not the paper’s 6%; and exactly the arithmetic no abstract performs.
Common ways factor implementations fail in production
- Tracking-error boredom: the tilt underperforms its benchmark for statistically normal multi-year stretches; capital’s patience, not the premium, is what breaks.
- Rebalance-date crowding: trading the same month-end as every indexed factor product.
- Definition drift: the live signal (vendor fundamentals, restatement handling) quietly differs from the paper’s CRSP/Compustat construction.
- The factor works; your version doesn’t: neutralizations and constraints reshape the bet until realized returns decorrelate from the published series.
Questions to ask
- What’s the premium under value-weighting, ex-micro-caps, net of the paper’s own turnover?
- Long leg, short leg, or spread — where does it actually accrue?
- What’s the borrow bill on the short decile today?
- What has the factor returned since publication?
What our scoring captures
The gates are the rigor axis’s practical half: papers reporting net-of-cost, capacity-bucketed, post-sample results occupy the top of the factor hub, and the quadrant system separates premium-documentation (academic) from premium-harvesting (implementable) papers cleanly. What no score provides is gates 4–5’s current state — crowding and decay are live variables; the archive dates every paper so you can apply the clock yourself.
The haircut arithmetic: turnover → · capacity → · The meta-evidence: factor-zoo papers →